The purpose of this study was to investigate the effect of using computer games in teaching mathematics on developing the number sense of fourth grade students. To achieve this purpose a study sample of (81) students was selected from the fourth grade. This sample was divided into two groups. One group was randomly chosen to be the experimental group that studied mathematics using computer games; the other was the control group that studied mathematics using traditional method and without using computer games. The instrument of the study was a number sense test. Data analysis procedures using One-Way ANOVA revealed a positive effect of using computer games in teaching mathematics on developing the number sense of fourth grade students.