Evaluation of Non-functional requirements (NFRs) of a software product is a key to achieve high quality software. Non-functional requirements define how a system should perform and capture required properties of a system, such as timing, and reliability. NFRs receive less attention during the software development life cycle than functional requirements, even though NFRs can lead to the failure of a system. Most of the analyzed models are only focused on a couple of non-functional requirements and they are complex to be understood and implemented. Also such models are mainly focused on modeling and capturing instead of evaluating. In order to address this problem, in this M.Sc. Thesis we propose a model for evaluating the software quality of the non-functional requirements of a software product. RNFs are based on the ISO/IEC 25023 standard. The proposed model can be implemented for evaluating any NFR. We represent the applicability of our model by using the SEMAT (Software Engineering Method and Theory) standard for representing software engineering practices and methods. We also use pre-conceptual schemas for representing the functionality of our model. Pre-conceptual schemas are developed to represent a specific domain anyone can use and understand.