Gynaephora qinghaiensis is a pest in the alpine meadows of the Qinghai-Tibet Plateau (QTP) that seriously harms grassland vegetation. Sexual dimorphism (SD) is common in insects, but its molecular mechanism at the tran scriptome level in insects, especially in G. qinghaiensis, has not been reported. In this study, we conducted transcriptome analysis of pupae and adults of the two sexes (male and female) of G. qinghaiensis. A total of 204,557,900 clean reads assembled into 114,944 unigenes were obtained by RNA-Seq. To explore differences in the transcriptome levels of molecular characteristics related to SD between the two sexes of G. qinghaiensis, gene expression profiling was performed. A total of 88 differentially expressed unigenes related to sex determination were found in the pupae of G. qinghaiensis; of these, 74 were upregulated and 14 were downregulated in the female pupae compared to the male pupae. Forty-five unigenes related to sex determination were found in the adults of G. qinghaiensis; of these, 15 were upregulated and 30 were downregulated in the female adults compared to the male adults. This indicated some differences in the expression of genes involved in sex deter mination between male and female individuals of G. qinghaiensis. Therefore, we speculated that sex-determining genes may play an important role in the formation of sexual dimorphism in G. qinghaiensis. Our report provides a valuable genomic resource for further studies of grassland caterpillars and improves our understanding of the molecular mechanisms underlying sexual dimorphism between male and female insects.