Baddeley’s grammatical reasoning test is a quick and efficient measure of fluid reasoning which is commonly used in research on cognitive abilities and the impact of stresses and environmental factors on cognitive performance. The test, however, is verbal and can only be used with native speakers of English. In this study, we adapted the test for application in the Persian language using a different pair of verbs and geometrical shapes instead of English letters. The adapted test had high internal consistency and retest reliability estimates. It also had an excellent fit to a one-factor confirmatory factor model and correlated acceptably with other measures of fluid intelligence and participants’ grade point average (GPA).