Syntax has a high importance among linguistic parameters, and syntax-related problems are the most common in language disorders. Therefore, the present study aimed to design a Photographic Expressive Persian Grammar Test for Iranian children in the age group of 4-6 years and to determine its validity and reliability. First, the target morphosyntactic structures among Persian-speaking 4-6-year-old children were extracted, and items related to each structure were designed. After both content and face validity were determined and modifications were applied, the initial version of the test was performed on 100 children. The final version of the test was performed on 400 eligible, typically-developing children selected using the random (cluster) method. Psychometric properties investigated in this study include construct validity (convergent validity and age and gender discriminative validity) and reliability (test-retest, inter-rater, and internal consistency). Content validity of each item was between 0.8 and 1, and content validity of the whole scale was 0.86. Exploration of construct validity suggested that age and gender affect the test scores. Convergent validity was found to be significant. Results of test-retest, and inter-rater reliability were significantly correlated and the test was found to have high internal consistency. The Photographic Expressive Persian Grammar Test with 40 items is the first reliable and valid scale that exclusively and accurately evaluates morphosyntactic characteristics of 4-6-year-old Persian-speaking children.