The relative abundances of bacteria and archaea in major oil-shale mines (Fushun Mine in Liaoning,Huadian Mine in Jilin and Maoming Mine in Guangdong) of China were investigated by fluorescence in situ hybridization (FISH) method,and three types of samples were collected from each mine,including sandy soil,freshly mined oil-shale and weathered oil-shale or underground sandstone. The optimal hybridization conditions of TRIzol and lysozyme were beneficial to increasing the hybridization rate when the hybridization temperature was 46°,the hybridization time was 2.5h,and the volume fraction of deionized formamide was 20%.In all samples,the relative abundances of bacteria and archaea are above 50% and below 5%,respectively,and the relative abundances of bacteria and archaea in the freshly mined oil-shale are the highest. The relative abundances of bacteria and archaea are different between any two mines: bacterial relative abundance in Huadian mine is the highest,followed by Maoming mine and Fushun Mine,but archaeal relative abundances are just the reverse.