Udemy is an online learning platform which contains more than 45000 instructional content. The aim of this study is to measure the usability level of Udemy platform in cases of effectiveness, efficiency and satisfaction. Case study method was employed in this study. 5 participants, that have never used Udemy before, between the ages of 17 and 21 were observed during the study. Questionnaires were implemented and interviews were done with the participants after the usability observation. Findings indicated that Udemy online learning platform was efficient and effective according to the participants. The average task completion time is 39.65 seconds and error rate is 15% according to the findings. Moreover, participations indicated their satisfaction about the online platform. Results and several recommendations were discussed at the end of the study.