A series of saturated hydrocarbons,including nalkanes,terpanes and steranes,have been identified in inhalable particulates (PM10) samples collected in northwestern urban district in Beijing by means of the GC and GCMS The parameters of the saturated hydrocarbons,such as major peak carbon number,carbon preference index (CPI) and hopane 22S/(22S+22R) ratios,have been calculated,which can beused to reflect the sources of the extractable organic matters in PM10 The nalkanes in PM10 samples from Beijing air have the major peak carbon numbersranging from 23 to 27 and the CPI values between 1 and 3,suggesting that the saturated hydrocarbons may be derived from both modern higher plants and incomplete combustion of fossil fuels (coal and petroleum )The results also show that the saturated hydrocarbons in the spring and summer PM10 samples are mainly from biomass such as higher plants,pollen and microbes,while the saturated hydrocarbons in the autumn and winter PM10samples are mainly from incomplete combustion offossil fuels  Many terpanes presented in PM10similarly indicate a source of incomplete combustion of fossil fuels such as petroleum Steranes detected in PM10imply that parts of saturated hydrocarbons may come from engine oil released by vehicles