Generalizability Theory (G-Theory) has become the gold standard of reliability analysis in OSCEs. However, little progress has been made in popularizing G-Theory. This method allows various variance calculations to determine and quantify the source of an error. EduG is the only GUI software able to calculate G-Theory. The objective of this project is to introduce the G-Theory analysis of an OSCE using EduG. This assessment is a one day OSCE consisting of 10 stations per circuit. There are 3 buildings used in this exam. Each building held one complete circuit. G coefficient is 0.76. The majority of error (81.4%) was due to the interaction between students (nested in location) and observations. There is no error coming from the observation itself. Mean from building A, B, and C are 57.41, 57.97, and 61.56, respectively. First conclusion, the possible source of error is greater in building C. Secondly, EduG is capable calculating the reliability analysis in OSCE using G-Theory.