The study focused on the effect of advance organizer and guided inquiry instructional strategies on SSI students’ in Ecology in Zone C, Benue State. Quasi experimental research design of non-randomized pre-test, post- test was used for the study. The population comprised of all SS 1 students in the Zone. Using purposive sampling technique, four schools were selected and a total of 146 students participated in the study. Student Interest Inventory (SII) was used for data collection. The reliability coefficient of SII on 50 students after trial testing using Cronbach alpha was found to be 0.82. Mean and standard deviation were used to answer the research questions while the hypotheses were tested at 0.05 significant level using ANCOVA. The study found mean difference between interest ratings of students taught with advanced organizer and those taught with guided inquiry strategy in favour of those taught with guided inquiry. The study also revealed that gender has significant effect on interest ratings of students in ecology using the two teaching strategies. It was recommended that ecology should taught using guided inquiry for students to be in control of learning and to arouse their interest of male and female students in ecology.