This study investigated the effects of mindmapping teaching strategy on senior secondary school students’ retention in Biology. Two research questions and three null hypotheses were formulated to guide the study. Quasi-experimental design (Non-equivalent control group design) was used. The population of the study comprised of 3785 senior secondary (SSS) biology students from the study area. A sample size of 129 SSS biology students was randomly sampled using simple random sampling techniques from four schools out of 12 coeducational Governments owned Senior Secondary Schools that were used for the study. The experimental group was taught selected biology concepts using mind mapping teaching strategies while the control group was taught with conventional method. The instrument for the study was Biology Achievement Test (BAT) which was developed by the researchers. The same instrument BAT was used for retention, the only difference was that the items were reshuffled. These instruments were validated by experts. This was used for data collection. The instrument was trail-tested for reliability using Kuder-Richardson (K-R 20) formular. Reliability index of 0.84 was obtained which guaranteed the use of the instrument for the study. The research questions were answered using mean and standard deviation, while Analysis of covariance (ANCOVA) was used to test the hypotheses at 0.05 level of significant. From the findings, it was observed that mind mapping teaching strategy enhanced retention more than the conventional lecture method, the result equally showed that female students slightly had a higher retention score than their male counterpart. This  indicated that exposure of students to mind mapping teaching strategy influenced both male and female students but the females retained a little more than the male students (7.02<9.7). The findings equally showed that the interaction effect of gender and method on students’ mean achievement scores in biology is not significant.