The study examined the effects of an Advance Organizer on secondary school students’ learning outcomes in Chemistry in Ekiti State. The pretest, posttest control group quasi-experimental design was adopted for this study. The treatment applied to the experimental group was Advance Organizer while the control group was exposed to the conventional method. The population for the study comprised of 19,603 Senior Secondary Schools Two (SSSII) students in 189 public Secondary Schools in the three senatorial districts across the sixteen (16) Local Governments Areas (LGAs) of Ekiti State. The sample for this study consisted of 144 SSSII Chemistry students found in intact classes of the schools selected for the study. The two instruments used for study were Chemistry Performance Test (CPT) and Chemistry Attitudinal Scale (CAS). The instruments were subjected to content and face validity. The reliability of the instruments was determined through the test re-test method and reliability coefficients of 0.87 and 0.85 were obtained for CPT and CAS respectively which were believed to be high enough to adjudge the instruments as internally consistent, stable and reliable enough for use. The results of the data collected from both pre-test and post-test were collated and analysed inferential statistics. Hypothesis 1 was tested using t-test, hypotheses 2 and 3 were analysed using Analysis of Variance (ANCOVA). Each hypothesis was tested at 0.05level of significance. The findings revealed that there is considerable improvement in the performance of students taught Chemistry using Advance Organizer compared with those taught using conventional teaching method; there is no significant difference in the performance mean scores of male and female students in Chemistry who are taught using advance organizer and those who are taught using conventional method. It was recommended that Advance Organizers should be employed for the teaching of Chemistry in secondary schools as innovative instructional strategy to bridges what students already know and what they are to learn. This will allow for teaching - learning interaction effectiveness.