Assembly will contain Namespaces, Classes, Data types it's a small unit of code for deployment. Assembly defines the name of the .dll file.It also avoids dll hell problem.
Namespace is used in order to avoid conflict of user defined classes.
Namespace:
1) it is a Collection of names wherein each name is Unique.
2) They form the logical boundary for a Group of classes.
3) Namespace must be specified in Project-Properties.
Assembly:
1) It is an Output Unit.
2) It is a unit of Deployment & a unit of versioning.
3) Assemblies contain MSIL code.
4) Assemblies are Self-Describing. [e.g. metadata,manifest]
5)An assembly is the primary building block of a .NET Framework application.
6) It is a collection of functionality that is built, versioned, and deployed as a single implementation unit (as one or more files).
7) All managed types and resources are marked either as accessible only within their implementation unit, or by code outside that unit.