The study investigated the effects of Advance Organizer teaching strategy on students’ academic performance and retention in Chemistry in Senior Secondary School in Ekiti State, Nigeria. The study was a pretest, posttest, control group quasi-experimental design. The sample for this study was 120 SSS II Chemistry students using multistage sampling procedure. The instrument used for this study was Chemistry Performance Test (CPT) and the treatment package used for the study was tagged: Advance Organizer Instructional Package (AOIP). Three null hypotheses were formulated and tested at 0.05level of significance. The data collected were analyzed using t-test and ANCOVA statistics. 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 and retention levels was found to be significantly better than that of the control group. This showed that Advance Organizer teaching strategy significantly influenced students’ academic performance and retention in Chemistry in senior secondary school. The implications of the results on students’ academic performance and retention in Chemistry are discussed. Based on the findings of the study, conclusion and recommendations were made.