Isonychia taishunensis Huang, Shen, Zhang & Cheng sp. nov. is described based on larval samples from Taishun County, Zhejiang Province, China. The new species is distinguished from other species of Isonychia Eaton by the following characters: gill plates with spines apically, the color of abdominal tergum X, color pattern of abdominal terga I-IX, and color pattern of each gill plate. The genetic distance between the new species and other species of Isonychia is over 10% using the Kimura 2-parameter model. The phylogenetic relationship of I. taishunensis is close to the clade of I. japonica Ulmer and I. ussurica Bajkova. The morphological characters and molecular data (COX1, Kimura 2-parameter) support that this new species represents the ninth species of the genus Isonychia in China. The modified key to known larvae of the genus Isonychia is provided.