The study investigated the effects of developed electronic instructional medium (video DVD instructional package) on students' achievement in Biology. It was guided by two research questions and two hypotheses, using a quasi-experimental, pretest-postest control group design. The sample comprised of 180 senior secondary, year two students from six schools located in the three education zones of Niger State. The subjects were divided into an experimental group (electronic medium instruction) and a control group (traditional lecture instruction). Structured Biology Achievement Test (SBAT) with internal consistency reliability co-efficient of 0.83 was used to measure the student's achievement before and after the treatment. The data obtained from the study were analyzed using Analysis of Covariance (ANCOVA). Results from Means, Analysis of Covariance (ANCOVA) and Scheffe test indicated that the achievement of students in biology greatly improved with the use of electronic instructional medium. Students' gender had no significant effect on their achievement in biology when electronic medium was used. These results have implications for innovative use of instructional media and creating sound strategies for disseminating science in the classroom.