The abstract should be in Palatino Linotype as the font type, 9 pt., between 150-250 words. The aim of this study was to investigate the effect of the 7E instructional strategy on the achievement and retention of SS II (11th grade) Biology students in public secondary schools in Nigeria. Intact classes of 60 students were randomly selected and denoted as the experimental group, which was taught with the 7E instructional strategy, and the control group, which was taught using the traditional, teacher-centered instruction methods. The data were collected via Biology Achievement in Respiration Test (BART), and analyzed using descriptive statistics and Independent Samples t-test for both variables. The results of the independent-sample t-test for the post-test scores indicated a significant value of p < 0.05 for the achievement variable. Similarly, the statistic indicated a p < 0.05 for students' retention, when taught by the 7E instructional approach. The implication of these findings suggest that the adoption of the 7E instructional approach enhances students' achievement in Biology. The findings also imply that students are able to remember what they were taught, after a time lapse, which enhances their chance of passing examinations. The retention test was administered a month after the post-test.