Objective: The purpose of this research is determining the instructional games effect on learning of some mathematics concepts in boy students with educable mentally retarded.

Materials & Methods: The method of this research is quasi-experimental. By convenient sampling two elementary schools mentally retarded boys were selected and all of their first grade students were assigned to experimental and control groups randomly (8 students in each group). The mathematical concepts presented to experimental group via instructional games and regulatory teaching style conduced to control group. The instruments consist of four investigator’s inventive instructional games, four investigator’s inventive sub-tests and an investigator’s inventive post-test. Data were analyzed by Mann-Whitney U test.

Results: There was significant difference between two groups in total score of mathematics concepts (P=0.025). As well as, the intervention caused increased the means of numbers in experimental group in each of concept than of control group, but their difference was not significant.

Conclusion: Instructional games can improve learning of mathematics concept in mentally retarded students.