The purpose of this study was to test the effectiveness of a courseware, ``Cell Division``, and to analyze students` and biology teachers` opinions on the courseware. Cell Division was the courseware which had computer simulation of cell division and developed by the authors for teaching the middle school students the process of cell division. Non-equivalent pretest-posttest control group design was used to test the effectiveness of the courseware. One hundred and forty-four 9th grade girl students were selected: 72 students for the experimental group and 72 students for the control group. The experimental group was required to use the courseware in the lesson and the control group was taught by teachers using the traditional chromosome model. One-way ANCOVA showed that the difference of learning achievements between the experimental group (courseware lesson group, n=72, adjusted mean=9.99) and the control group (teacher lesson group, n=72, adjusted mean=8.87) was statistically significant (F=7.584, p=0.007). The analysis of students` opinions of the experimental group and 32 biology teachers` opinions about the courseware revealed that the courseware was helpful and useful in the learning and teaching cell division.