Objective High PM2.5 concentration is the main feature of increasing haze in developing states,but information on its microbial composition remains very limited.This study aimed to determine the composition of microbiota in PM2.5 in Guangzhou,a city located in the tropics in China.Methods In Guangzhou,from March 5th to 10th,2016,PM2.5 was collected in middle volume air samplers for 23 h daily.The 16S rDNA V4 region of the PM2.5 sample extracted DNA was investigated using high-throughput sequence.Results Among the Guangzhou samples,Proteobacteria,Bacteroidetes,Firmicutes,Cyanobacteria,and Actinobacteria were the dominant microbiota accounting for more than 90％ of the total microbiota,and Stenotrophomonas was the dominant gram-negative bacteria,accounting for 21.30％-23.57％.We examined the difference in bacterial distribution of PM2.5 between Beijing and Guangzhou at the genus level;Stenotrophomonas was found in both studies,but Escherichia was only detected in Guangzhou.Conclusion In conclusion,the diversity and specificity of microbial components in Guangzhou PM2.5 were studied,which may provide a basis for future pathogenicity research in the tropics.