This study examined the effects of computer animation instructional package on secondary school students' achievement in practical biology in Ilorin, Nigeria. The study adopted a pre-test, post-test, control group, non-randomised and nonequivalent quasi-experimental design, with a 2x2x3 factorial design. Two intact classes from two secondary schools were purposively sampled. The instruments used were Biology Practical Achievement Test (BPAT) for data gathering and Computer Animation Instructional Package (CAIP) as the treatment instrument. The reliability coefficient of BPAT was determined using the Pearson Product Moment Correlation and was found to be 0.91. Two research questions and two hypotheses were formulated in the study. The hypotheses were tested with t-test statistics at a significance level of 0.05. The study concluded that CAIP significantly improved students' achievement in practical biology. The researchers recommend that biology teachers should employ computer animation instructional packages to teach the practical aspects of photosynthesis among other biology topics.