diff --git a/facho/model/__init__.py b/facho/model/__init__.py
index 51a9345..f64bd55 100644
--- a/facho/model/__init__.py
+++ b/facho/model/__init__.py
@@ -1,4 +1,5 @@
 from .fields import Field
+from collections import defaultdict
 
 class ModelMeta(type):
     def __new__(cls, name, bases, ns):
@@ -20,6 +21,19 @@ class ModelBase(object, metaclass=ModelMeta):
         obj._fields = {}
         obj._text = ""
         obj._namespace_prefix = None
+        obj._on_change_fields = defaultdict(list)
+        
+        def on_change_fields_for_function(function_name):
+            # se recorre arbol buscando el primero
+            for parent_cls in type(obj).__mro__:
+                parent_meth = getattr(parent_cls, function_name, None)
+                if not parent_meth:
+                    continue
+                
+                on_changes = getattr(parent_meth, 'on_changes', None)
+                if on_changes:
+                    return on_changes
+            return []
 
         # forzamos registros de campos al modelo
         # al instanciar
@@ -28,7 +42,12 @@ class ModelBase(object, metaclass=ModelMeta):
                 if hasattr(v, 'default') and v.default is not None:
                     setattr(obj, key, v.default)
 
-
+                # register callbacks for changes
+                function_name = 'on_change_%s' % (key)
+                on_change_fields = on_change_fields_for_function(function_name)
+                for field in on_change_fields:
+                    obj._on_change_fields[field].append(function_name)
+        
         return obj
 
     def _set_attribute(self, field, name, value):
diff --git a/facho/model/fields/__init__.py b/facho/model/fields/__init__.py
index 4e35a11..c3f59a3 100644
--- a/facho/model/fields/__init__.py
+++ b/facho/model/fields/__init__.py
@@ -6,3 +6,15 @@ from .virtual import Virtual
 from .field import Field
 
 __all__ = [Attribute, Many2One, Model, Virtual, Field]
+
+def on_change(fields):
+    from functools import wraps
+    
+    def decorator(func):
+        setattr(func, 'on_changes', fields)
+
+        @wraps(func)
+        def wrapper(self, *arg, **kwargs):
+            return func(self, *arg, **kwargs)
+        return wrapper
+    return decorator
diff --git a/facho/model/fields/attribute.py b/facho/model/fields/attribute.py
index 9d8677c..6adfc36 100644
--- a/facho/model/fields/attribute.py
+++ b/facho/model/fields/attribute.py
@@ -16,4 +16,6 @@ class Attribute(Field):
     def __set__(self, inst, value):
         assert self.name is not None
         self.value = value
+        
+        self._changed_field(inst, self.name, value)
         inst._set_attribute(self.name, self.attribute, value)
diff --git a/facho/model/fields/field.py b/facho/model/fields/field.py
index 6d8e523..d340bbc 100644
--- a/facho/model/fields/field.py
+++ b/facho/model/fields/field.py
@@ -39,3 +39,8 @@ class Field:
             self._set_namespace(obj, self.namespace, inst.__namespace__)
             inst._fields[self.name] = obj
             return obj
+
+    def _changed_field(self, inst, name, value):
+        for fun in inst._on_change_fields[name]:
+            getattr(inst, fun)(name, value)
+            
diff --git a/facho/model/fields/function.py b/facho/model/fields/function.py
index 58388e5..1da5e52 100644
--- a/facho/model/fields/function.py
+++ b/facho/model/fields/function.py
@@ -31,4 +31,5 @@ class Function(Field):
 
     def __set__(self, inst, value):
         inst._set_field(self.name, self.field)
+        self._changed_field(inst, self.name, value)
         self.field.__set__(inst, value)
diff --git a/facho/model/fields/many2one.py b/facho/model/fields/many2one.py
index d75e03b..5134e3d 100644
--- a/facho/model/fields/many2one.py
+++ b/facho/model/fields/many2one.py
@@ -25,6 +25,7 @@ class Many2One(Field):
             setter(inst_model, value)
         else:
             inst_model._set_content(value)
-
+            
+        self._changed_field(inst, self.name, value)
 
 
diff --git a/tests/test_model.py b/tests/test_model.py
index 1028803..532c582 100644
--- a/tests/test_model.py
+++ b/tests/test_model.py
@@ -364,3 +364,38 @@ def test_field_inserted_default_nested_many2one():
     person = Person()
     assert '<Person><ID>ole</ID></Person>' == person.to_xml()
 
+def test_model_on_change_field():
+    class Hash(facho.model.Model):
+        __name__ = 'Hash'
+
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+
+        react = fields.Attribute('react')
+        hash = fields.Many2One(Hash)
+
+        @fields.on_change(['hash'])
+        def on_change_react(self, name, value):
+            assert name == 'hash'
+            self.react = "%s+4" % (value)
+
+    person = Person()
+    person.hash = 'hola'
+    assert '<Person react="hola+4"><Hash>hola</Hash></Person>' == person.to_xml()
+
+def test_model_on_change_field_attribute():
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+
+        react = fields.Attribute('react')
+        hash = fields.Attribute('Hash')
+
+        @fields.on_change(['hash'])
+        def on_change_react(self, name, value):
+            assert name == 'hash'
+            self.react = "%s+4" % (value)
+
+    person = Person()
+    person.hash = 'hola'
+    assert '<Person react="hola+4" Hash="hola"/>' == person.to_xml()
+