[Objectives]  To investigate the chromosome number of Ophiocordyceps sinensis, an important edible and medicinal fungi endemic to Tibetan Plateau and surrounding areas of high elevation, and thereby lay a foundation for genome sequencing and other research on the evolution, genetics and molecular biology of this species, as well as help determine the chromosome number of other entomogenous fungi. [Methods]  A genome assembly using second and third generation sequencing technology supplemented with Hi-C data, in addition to microscopic observation, was used to determine the chromosome number of O. sinensis. Strain 1229, the genome of which has been sequenced and assembled to a complete level, was cultured in insect cell culture medium to acquire blastospores. Blastospores were co-incubated with colchicines, then treated with lywallzyme to obtain dispersed metaphase chromosomes. Those chromosomes were stained with fluorescent DAPI, then observed and counted under a laser confocal microscope. [Results]  Based on the genome assembly obtained from second and third generation sequencing and Hi-C data, strain 1229 of O. sinensis was found to possess six chromosomes with a strong telomere interaction between chromosomes. This number was supported by microscopic observations. [Conclusion]  The genome of O. sinensis possesses six chromosomes. Blastospores are suitable for counting the chromosomes of O. sinensis.