Abstract: This study evaluated the effects of personalised system of instruction on students` academic achievement in Chemistry. The study also investigated the moderating effect of gender on the students` academic achievement. One hundred and nine senior Secondary School One (SS 1) students randomly selected from three co-educational secondary schools in Oro, Kwara State, Nigeria participated in the study. The study adopted a pretest, posttest, control group experimental design with a 3�2 factorial matrix. There were two experimental groups in which one received personalised instruction with target dates and the other without target dates. The control group received conventional teaching. Treatment lasted six weeks. Four hypotheses were tested at the .05 level of significance. The results of the analysis done using ANCOVA and Fisher`s LSD test indicated that students in the PSI group had more significant improvement in their academic performance in chemistry than those taught with conventional method. Also there was no significant interaction of treatment and gender on the dependent measure. Implications of the findings for counselling and educational practices and preparation of teachers on the use of PSI for improving students` learning were discussed.