This study investigated the effect of outdoor laboratory activity on student interest and academic achievement in biology among secondary school students in Abakaliki, Ebonyi State. The study employed a quasi-experimental research design, specifically the pre-test, post-test, nonequivalent control group, using two intact classes from separate schools. The sample consisted of 58 students, with 28 students in the experimental group and 30 in the control group. The instruments for data collection were the Biology Achievement Test (BAT) and the Biology Students’ Interest Inventory (BSII). The experimental group was taught using outdoor laboratory activities, while the control group received instruction through the conventional lecture method. The data collected were analyzed using mean, standard deviation, and Analysis of Covariance (ANCOVA) statistics. The findings revealed that students in the experimental group showed a greater interest in biology and significantly higher academic achievement compared to their counterparts in the control group. The study concluded that outdoor laboratory activities are an effective instructional strategy for enhancing students’ active and sustainable interest in biology. Based on these findings, it was recommended that biology teachers integrate outdoor laboratory activities into their teaching, and that school administrators and the government provide the necessary resources to support such practical approaches to science education.