Abstract: Field experiments of using Metarhizium flavoviride ultra low volume oil spray to control grassland grasshoppers were carried out in Inner Mongolia in 1999. Results showed that the oil spray was effective to all the 5 species of grasshoppers, namely, Oedaleus decorus asiaticus B. Bienko, Angaracris rhodopa (F. W.), Dasyhippus barbipes (F. W.), Bryodema luctuosum luctuosum (Stoll) and B.tuberculatum dilutum (Stoll). 8 d after application, 48.0% of O.decorus asiaticus was killed and the mortality increased to 88.1% at the end of 12th day. New spores of the green fungus appeared on the dead locusts 7~10 d later. It was probable that the spores emerged from the locust cadaver would infect those locusts which had escaped the fungal spray.