In this study, it is aimed to design a computer game for the 7th grade Science lesson and evaluate the effect of the computer game on students’ motivation and aggression. The quasi-experimental method has been selected as a quantitative method of research. The study group of the research is comprised of 444 7th grade students in total studying in 7 different schools chosen from each region of Turkey. In this context, while there is no interference in one of the two 7th grade classrooms from each school, the other is sustained with a computer game as an additional material to the teaching process. The application proceeded through 2014-2015 academic year. Motivation towards Science and aggression scale have been applied to all groups three times; at the beginning of the first term, at the beginning of the second term and at the end of the second term. As a result of the research, the computer game is found to generate a meaningful difference on behalf of the experimental group and to have no effect on aggression. Computer games meet the deficiencies of a conventional educational system by promoting learning via games and creating an engaging atmosphere helping students increase their motivation.