In this thesis, we discuss a method of applying assertion techniques to software requirements analysis to enhance the reliability of the requirements specification. Assertions are used for expressing the user's intention and the constraints imposed on the software requirements. An assertion language is designed by augmenting assertion facilities to the Requirements Specification Language(RSL) and thus has the same domain of discourse as RSL. This assertion language takes the form of Entity-Relationship Calculus which is based on the Entity-Relationship model and the predicate calculus. Describing assertions and their processing of the model constraints require semantic analysis. Therefore, we have incorporated an assertion processor into the existings requirements analysis system.