In this study, the researcher examined the influence of gender on hours of supervised library use on students’ performance in senior secondary schools in Imo State. Four objectives, four research questions were posed and four hypotheses formulated in the study. The study was carried out using quasi-experimental design which involved pre-test, treatment and post-test of non-equivalent group method. The population of the study was 94,963 Senior Secondary School Students (SS1-SS3) from 275 public secondary schools in Imo State. The sample size for the study comprised of 127 senior secondary II students drawn from three senior public secondary schools in Imo State. Purposive and cluster sampling techniques were used. Two instruments were used for collecting data for the study. The instruments were: English Language Achievement Test (ELAT) and Mathematics Achievement Test (MAT). The reliabilities of the instruments were established using Kuder Richardson formula 20 (KR-20) which yielded reliability coefficients of 0.73 and 0.71 for ELAT and MAT respectively. Research questions were answered using mean and standard deviation while two-way Analysis of Covariance (ANCOVA) was used to test the hypotheses at 0.05 level of significance. It was revealed hours of supervised library use increased the achievement of male students more than the female students in English Language but not significantly different; hours of supervised library use increased the achievement of male students more than the female students in Mathematics significantly and there is no significant interaction effect of gender and hours of supervised library use on the achievement mean scores of the students both in English Language and Mathematics. Based on the findings, it was recommended among others that since hours of supervised library use have been found to enhance the quality of achievement in English Language and Mathematics for male students, teachers should be encouraged to employ it more in the teaching of the subjects. By so doing, the achievement of students in these subjects could be enhanced. Also gender should not be a determining factor in students’ achievement since it does not have a significant interaction effect on the achievement of students in these core subjects.