This study investigated the effects of inquiry based learning on students' retention in senior secondary school biology. Two research question guided the study. A quasi experimental research design was adopted. 216 SSS2 biology students in Ikwo Local Government Area of Ebonyi State, South East of Nigeria were used in the study. Data were collected using Biology Retention Test (BRT) validated by experts in Biology Education and Measurement and Evaluation BRT had reliability index of 0.92 as determined using kuder-Richardson formula 20 (K-R 20) reliability coefficient. Findings of the study revealed that inquiry based learning has positive effects on students’ retention in biology. Again, inquiry based learning favours female students’ retention in biology than the male students Recommendations made include, teachers should adopt the inquiry based learning method to teach students. Also training and re-training of teachers in the use of inquiry based teaching should be organized for teachers by professional bodies such as the Science Teachers Association of Nigeria and the Ministry of Education. Key Words: Inquiry Based learning, Retention, Biology, Senior Secondary School