A quasi experimental study was conducted for six weeks to determine the effectiveness of two different 3D computer simulation based teaching methods, that is, realistic simulation and non-realistic simulation on Form Four Biology students' achievement and memory retention in Perak, Malaysia. A sample of 136 Form Four Biology students in Perak, Malaysia were involved in this study. Students from two Form Four Biology classes were randomly selected for this study. One class was randomly assigned as the treatment group (68 students) while the second Biology class was the control group (68 students). Pre-test was given to all students before they underwent the teaching and learning process for the topic on Cell Division. The students in the treatment group were taught Cell Division using realistic simulation while the control group students learnt using non-realistic simulation for three weeks. All students were given post achievement test during the third week after they have learnt the Cell Division topic. Post memory retention test was given to all students on the sixth week that is three weeks after the post achievement test. Data of the present study was collected and analyzed using descriptive statistics and inferential statistics such as paired samples t-test and one way ANCOVA. The results show that realistic simulation is a more effective 3D computer simulation based teaching method than the non-realistic simulation and it improves Biology students' achievement and memory retention.