The quest for the effective methods of teaching social studies in Nigerian schools is a continuous one. This research is designed to investigate the effects of integrated group based mastery learning Approach in the teaching of social studies in Junior Secondary Schools in Benin Metropolis. The problem of learners’ poor performance and underachievement in social studies has been a major issues of concern and interest in the Nigeria educational sector. Two research questions were raised with two corresponding hypotheses to guide the study. A quasi-experimental design of non-equivalent control group was adopted. Two mixed secondary schools were purposively selected from Benin City, out of which, two in-tact classes were selected. The instrument used for the data collection was the Social Studies Achievement Test (SSAT). The data collected were analyzed using t-test of independent sample. The result showed that there was a significant effect of treatment on social studies students achievement. This means that the integrated group based mastery learning model was more effective than the traditional expository method. It is recommended that through in-service training, seminars or other forms of on-the-job training to employ mastery learning models.