Abstract: In 2007 and 2008, Pythium root rot of turf grass was surveyed in 13 district of Lanzhou City. The incidence in the most seriously affected fields was 83.33% with a disease index of 36.67. The disease caused three types of symptoms on the turf grasses depending on: Leaf tip blight, leaf middle shrink and rhizome-brown rot. The chief pathogen, based on morphology, cultural characteristics, and pathogenicity, was identified as P. aphanidermatum with an isolation frequency of 100% from rhizomes. The incubation period for P. aphanidermatum is 14-15 h at 35℃ with a relative humidity of 90%.