The aim of this research is to examine the effectiveness of intelligence games (IG) on mathematical reasoning abilities (MRA) and mathematics achievement scores of students. For this purpose, mathematical reasoning pre-test was given to three groups of 6th grade middle school students, and then, after the experimental group was given a training program that included all the contents of the IG course curriculum, a mathematical reasoning post-test administered in all groups. The data obtained were evaluated with SPSS 25 package program, ANOVA and ANCOVA analyses. According to the analysis, since the difference between the groups' mathematical reasoning pre-test scores was statistically meaningful, the post-test results were evaluated with ANCOVA. According to the results of the evaluation of the post-test points of the participants, the difference between the experimental group and the control 2 group was found to be statistically significant and this was interpreted as a positive development in the MRA of the students who received IG training. While there found not any significant differences between the MRA posttest points of the groups participating in the study and their genders, a significant difference was found between their math course achievement grades. This was interpreted as a meaningful affect in the math course grades the students who received IG training. Based on the study, it can be suggested that due to the important influence of IG on MRA, it may be useful to integrate them into the activities in mathematics courses conducted at school.