Participating in comparative international studies such as TIMSS, which examines and compares the efficiency and effectiveness of curricula and textbooks of different countries, is a method to identify the strengths and weaknesses of the textbooks of the participating countries. Since Japan, like Iran has a national curriculum, and in different periods of TIMSS, has a higher performance than Iran, so it was chosen to be compared with Iran. This research aimed at comparing the released problems of TIMSS 2019 with the content and problems of the first to fourth grade mathematics textbooks of Iran and Japan. In this study, the English version of Japanese textbooks has been used. The research population included the mathematics textbooks of the 1^st to 4^th grades of Iran and Japan, as well as the 10 released problems of TIMSS 2019. It was a descriptive-analytical-comparative study. The results showed that 6 out of these 10 problems, have similar examples in Iranian textbooks and Japanese textbooks have 5 problems similar to these 10 problems. Also, the results showed that regardless of whether or not similar content and problems were presented in the textbook, in all problems, the percentage of correct answers of Iranian fourth grade students were lower than that of Japanese students, except for the problem on the symmetry. Considering the different cognitive domains of TIMSS problems, regardless of the cognitive domain of the proposed problem, except for the symmetry problem, Iranian students' performance was lower than their Japanese counterparts. Math teachers can use the results of this research.