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The objective of this study was to determine the prevalence,species and subtypes of Cryptosporidium infecting yaks in the Qinghai Province of Northwestern China.The prevalence of Cryptosporidium spp.was detected by microscopy and nested:PCR.A total of 586 fecal samples were collected from yaks in 6 counties,of which 142 (24.2%) samples tested positive for Cryptosporidium.The small subunit (SSU) rRNA gene of fifty:five samples were amplified and sequenced successfully and demonstrated that Cryptosporidium bovis (31/55,56.4%)was the most common species,followed by C.parvum (16/55,29.1%) and C.ryanae (5/55,9.0%).Mixed infections of C.parvum and C.bovis (n=2),C.ryanae and C.bovis (n=l) were also detected.All three species were found in yaks ranging in age from < 1 year,1:2 years,to >2 years.Cryptosporidium was most commonly detected in spring (28.4%),followed by summer (20.9%),then winter (17.5%).Cryptosporidium parvum positive samples were subtyped using the 60 kDa glycoprotein (gp60) gene.Subtypes ⅡaA 15G2R 1 (n=8),ⅡaA 16G2R 1 (n=2),ⅡaA 14G 1R 1 (n=1),ⅡaA 14G2R 1 (n=1) and ⅡaA 16G3 R 1 (n=1) were detected.All of these subtypes are zoonotic,and may pose a potential threat to human health.