The study was conducted to determine the effects of instructional material on the performance of Junior Secondary School students in Integrated science in Ondo State. The study used a quasi-experimental design with a pre/post-test randomized control group arrangement. A sample of 40 students was used for the study. To guide the study, two specific objectives and four null hypotheses were tested at 0.05 level of significance. Students’ achievement test in Integrated science(SATPA) was developed to gather data for the study. The instrument was validated by integrated science teachers in junior secondary schools and the reliability coefficient of 0.80 was obtained using K-R 21. Data were analyzed and hypotheses were tested using t-test and Analysis of covariance (ANCOVA). The findings of the research indicated that there was a significant difference between the performance of students taught with instructional chart and those without and there was significant difference between the performance of students taught with instructional pictures and those taught without it among other findings. Based on the findings, it was recommended that teachers should use instructional materials in teaching integrated science where practical demonstration is not visible in order to enhance effective teaching and learning among other recommendations.