The goal of the research was to develop a method to prioritize both functional and non-functional requirements in software development simultaneously. The Integrated Prioritization Approach (IPA) was created to integrate the prioritization process for these two types of requirements. By using triangular fuzzy numbers and weighted average decision matrix, IPA was able to produce prioritized lists of requirements. Two experiments showed that IPA outperformed other approaches in terms of time consumption, accuracy, and ease of use.