This study was designed to determine the effect of computer simulation instructional strategy on primary school pupils' achievement in basic science in Akure township in Ondo state, Nigeria. Constructivist theory was used as the framework, while the study adopted pretest-posttest control group quasi-experimental design. Four primary schools were randomly selected from Akure township in Ondo state, Nigeria, a total of four intact classes were used. A total of 151 primary IV school pupils (71- experimental group, 80--control group) participated in the study. Instruments used were instructional guides, Pupils' Basic Science Achievement Test (r =0.82) and Pupils' Basic Science Self-Efficacy Questionnaire (alpha=0.80). The study lasted 8 weeks. Data were analysed using Analysis of covariance and Estimated marginal means. There was a significant main effect of treatment on primary pupils' achievement in basic science F[subscript (1,146)]=632.99; partial n[superscript 2]=0.81). The pupils exposed to computer simulation strategy had a higher basic science achievement mean score (19.60) than their counterparts in the convention strategy (12.13). Computer simulation instructional strategy enhanced primary pupils' achievement in basic science in Akure township in Ondo state, Nigeria. Primary school teachers should adopt this strategy to improve primary school pupils' knowledge of basic science.