This project is on Effect of demonstrational instructional strategy on senior secondary school students’ academic achievement in biology. The study investigated the Effects of Demonstrational Instructional Strategy on Senior Secondary School Students Academic Achievement in Biology. This study became necessary because of the unavailability of instructional materials for teaching biology in secondary schools. The study employed a quasi-experimental design, specifically the pretest-posttest non-equivalent group design. One hundred students from comprised of males and females randomly selected from the senior secondary one students. The one hundred students shall be up to (50) fifty male and female students for the sample of the study. The experts validated the instrument Biology Achievement Test (BAT). Three research questions were answered and two hypotheses were tested. The data were analyzed using mean, standard deviation. The results revealed that students taught using demonstrational instructional strategy materials performed better than students taught using conventional materials. Male students did not perform better than their female counterparts in Biology. Rural students performed better than urban students in biology. The results do not suggest ordinal interaction effects between mode of method and gender on students’ achievement in biology.