The present study aimed to identify seasonal macrobenthos abundance in the Jajrood River. The diversity of macrobenthos in the Jajrood River was identified and studied at five stations in the autumn and winter of 2014 and spring and summer of 2015. The geographical location of each station was determined by GPS. Samples were collected and examined seasonally. Five orders, 15 families, 17 genera, and 19 species of macrobenthos were identified in the study conducted in the Jajrood River. The highest and the lowest frequencies belonged to Insecta and Crustaceae with 72% and 0.2% of the total frequency, respectively, among the five orders identified in the Jajrood River. Among the identified species, Chironomus sp. and Tipula sp. with total frequencies of 865 and 3 per square meter, respectively, presented the highest and the lowest abundances. The density of macrobenthos fluctuated in the autumn and winter with maximum and minimum densities of 1073 and 801 per square meter, respectively. The families identified in this sampling belonged to the orders Insecta (9), Gastropoda (2), Malacostraca (1), Cructaceae (1), and Oligochaeta (2).