This paper provides a research of Object-Oriented requirements modeling. The proposed OO modeling strategy is based on the semantics and the diagram notation of the UML. The semantics of the UML formalizes the expression of the user requirements, and the diagram notation also enhances the understandability, trace-ability, verifiability, and modifiability of the requirements model. The ability of the system will greatly beneficent the end-users, and the analysts who participate in the activity of the whole life cycle of the Requirements Engineering. To demonstrate the viability of the approach, we take an example of a Small Byte Subscription System.