The main aim of this research was to investigate the effect of computer games on student' critical thinking disposition and educational achievement. The research method was descriptive, and its type was casual-comparative. The sample included 270 female high school students in Andimeshk town selected by multistage cluster method. Ricketts questionnaire was used to test critical thinking and the researcher made questionnaires were used to test computer games. T-test and one-way ANOVA were employed to analysis of the data. The findings of the study showed that playing computer games has no significant effect on critical thinking, however, there were a significant effect of playing computer games on students' educational achievement (P<0/05). Furthermore, the results showed that the type of computer game has no significant effect on students' disposition to critical thinking and their educational achievement.