Abstract Abstract: 【Aim】This study aims to provide the basic scientific data of aquatic insect species in Inner Mongolia and a solid base for their potential application in freshwater quality monitoring and protection by the government and scientists in the future. 【Methods】Benthic aquatic insects were sampled by using a qualitative collection method and the water quality was assessed by the family biotic index (FBI), EPT species richness and Shannon-Wiener biodiversity index.【Results】Of 187 freshwater insect species in 72 genera, 59 families, 7 orders collected in the 52 localities, 1 species was new to science; 2 families, 3 genera and 25 species were newly recorded in Inner Mongolia; 1 genus and 2 species were recorded for the first time in China; and 56 additional species are under identification. The diversity of Trichoptera and Ephemeroptera were the highest while that of Plecoptera was the lowest in recorded 7 orders; the proportions of families and individuals of the two orders accounted for 42.37% and 84.29%, respectively, so Trichoptera and Ephemeroptera are dominant groups among the seven orders. The localities of rich species diversity were distributed mainly in the eastern Inner Mongolia, including Hulunber, Hinggan League, Tongliao and Chifeng. The water quality ranks assessed by the family biotic index, EPT species richness and Shannon-Wiener biodiversity index showed that the evaluation results of FBI and EPT species richness were similar, but differed greatly from that of Shannon-Wiener biodiversity index. 【Conclusion】 There are more abundant species of Trichoptera and Ephemeroptera with lower tolerance value in Inner Mongolia, so the caddisflies and mayflies are more suitable and better candidates as indicators of water quality in this region.