Despite the widespread use of Massive Open Online Courses (MOOCs) in online learning, the usability of MOOC portals remains a major challenge. While expert heuristic evaluation principles have been proposed as a potential solution to usability problems, there is a lack of research on the effectiveness of these principles in a real-life and big-size project context. This case study examines the usability test process derived from expert heuristic evaluation principles within a national MOOC portal context and identifies how a collaborative approach can be used to enhance the effectiveness of usability testing. Since MOOCs meet the needs of the learners by keeping the investment to a minimum and creating close links to user interaction, we, as instructional designers, experienced a continuous and sequentially usability test process from the beginning of the design stage tests of 100 MOOCs to the end-user test phases. That’s why the mainly expert heuristic and collaborative approach (EHCA) is used for finding the usability problems in an iterative design process as Nielsen emphasized. Between 2015-2017, a distinctive, ongoing procedure based on immediate feedback and reliability was performed by both instructional designers (n=8), online learning experts (n=4), quality assurance testers (n=4) and end users (n=10) through Nielsen's major test components (learnability, efficiency, memorability, errors, and satisfaction). The test documents were collected, semi-structured interviews were done, testing processes were observed throughout the MOOC portal creation process, and the “collaborative approach” focusing on more expert collaboration and gradual evaluation, immediate feedback, and revised test procedure, and more prototypes and fewer problems were embraced. This approach which answers the question of “how to make a more effective evaluation of the usability of the MOOC portal” can be considered a prototype of a structure that can give new design suggestions over the years. One of the contributions of the study can be summarized as providing the relationships between the expert heuristic and collaborative approach with real-life and big-size project evidence. So, the implications made for theory and practice have the potential to make critical contributions to the usability test process. Hence, in this study, we tried to offer a flexible and collaborative usability testing process with expert team members and several methods to minimize the effort and time for testing by always dealing with the usability problems of MOOC portals during the process. Therefore, the outputs of this study can be beneficial to various MOOC portals or any kind of online learning platform in terms of sustainability and efficiency.