The study investigated the effects of concept mapping on students' achievement in basic science. The study was carried out in Ebonyi State of Nigeria. The study employed a quasi-experimental design. Specifically the pretest posttest non-equivalent control group research design was used. The sample was 122 students selected from two secondary schools drawn from the population through a simple random sampling. One school was used for treatment and the other for control. The treatment group was taught basic science with concept mapping approach while the other was taught with conventional method. Three research questions and three null hypotheses guided the study. Mean, standard deviation and the Analysis of Co-Variance (ANCOVA) were used to analyze data. Results showed that concept mapping fosters students' achievement in basic science than conventional method. It boosts the achievement of both male female students in the subject. In addition there is no interaction between gender and teaching methods on students' achievement in basic science.