Abstract: [Objective] Investigation of ammonia-oxidizing microorganisms (AOMs) in hot springs is of significant importance to understand global nitrogen cycling. However, we still know little about the abundance of AOMs in hot springs. In this research, the abundance of AOMs in thirteen hot springs located in Yunnan Province, China, and the effects of environmental variables (e.g. temperature, pH and ammonia concentration, and certain ions) on the AOM abundance were studied. [Methods] Microbial abundance in collected hot spring samples was determined by using an integrated approach including reverse-transcription quantitative polymerase chain reaction and catalyzed reporter deposition-fluorescence in situ hybridisation. [Results] Total biomass in the collected hot spring samples was 108-109 cells/g, among which ammonia-oxidizing archaea (AOA) occupied 0.02-1.32%, whereas no ammonia-oxidizing bacteria were detected. Statistical analysis indicated that AOA abundance was significantly（p<0.05）correlated with concentrations of NH3, NO2-, NO3-, pH and temperature, but not related (p>0.05) to salinity and concentrations of Fe2+ and salinity. [Conclusion] AOA were the major component of AOM in the studied hot springs, and play an important role in ammonia oxidation in hot springs. Multiple environmental variables (e.g. NH3, NO2-, NO3-, pH and temperature) were together controlling the AOA distribution among hot springs of different conditions, and some environmental variables, such as Fe2+ and salinity may not be the key factors for AOA in hot springs.