[Objectives]  The cellular immune response of Thitarodes xiaojinensis does not prevent infection by Ophiocordyceps sinensis and therefore provides a distinct and valuable model for studying the immune interaction between host insects and entomopathogenic fungi. The aim of this study is to investigate the effects of O. sinensis infection on the morphology of T. xiaojinensis hemocytes and the transcription levels of genes related to pseudopodia formation. [Methods]  A scanning electron microscope and laser scanning confocal microscope were used to observe and compare differences in hemocyte morphology between healthy and O. sinensis-infected T. xiaojinensis. Real-time quantitative PCR was used to detect transcriptional changes in genes involved in microfilament synthesis in hemocytes before, and after, infection with O. sinensis. [Results]  The formation of filopodia and lamellipodia in T. xiaojinensis hemocytes was inhibited after infection by O. sinensis. Expression of the DRF gene (promoting microfilament assembly) was also significantly down-regulated (P<0.01) and thymosin (a microfilament assembly inhibitor) was significantly up-regulated (P<0.01). [Conclusion]  The microfilament assembly of T. xiaojinensis hemocytes was inhibited by infection with O. sinensis, preventing formation of hemocytes’ filopodia, thereby allowing the fungus to circumvent the host cellular immunity.