The research aims to examine the effect of educational game activities on academic achievement in secondary school 5th -grade science lessons. The study group of the research consists of 71 5th-grade students studying at a public school in Turkiye in the 2017-2018 academic year. In the research, the pretest and post-test comparative design group, which is one of the quantitative research methods, was used to achieve the research objectives. A random sampling technique was used to determine these two groups. In the experimental group (EG), the lessons were enriched with educational game activities (EGA). The control group (CG) taught the courses based on the current science teaching program (CSTP). An academic achievement test (AAT) has been prepared for the unit goals of the 5th-grade science course "Spreading of Light". AAT was applied to the groups before and after the experiment independed samples t-test and Whitney u-test were used in the analysis of the data. The data showed that the EGA used in the science course has a positive effect on academic achievement.