The study investigated the effects of Advance Organizer teaching strategy on students’ academic performance in Biology in Senior Secondary School in Ekiti State, Nigeria. The study was a pretest, posttest, control group quasi-experimental design. Purposive and stratified random sampling techniques was used to select a total sample of 80 SS II Biology students (this sample was divided into experimental and control groups in ration 1:1 i.e 40 in each group) from two Senior Secondary Schools in Ikole Local Government Area, Ekiti State. Three null hypotheses were formulated and tested at 0.05 level of significance. The instrument for this study was Biology Achievement Test (BAT) and the treatment package used for the study was tagged: Advance Organizer Instructional Package (AOIP). The data collected were analysed using t-test and ANCOVA statistical analysis packages. The results of the analyses showed that no significant difference existed between the performances of students in experimental and control groups involved in the study at pretest. However, students’ achievement in the experimental group at post-test level was found to be significantly better than that of the control group. This showed that Advance Organizer teaching strategy significantly influenced students’ academic performance in Biology in senior secondary school. The implications of the results on students’ academic performance in Biology are discussed. Based on the findings of the study, conclusion and recommendations were made.