Abstract: The air-borne microbial concentrations over the sea areas around Hainan Island and Western Guangdong, and over two cities of Hainan Island were measured by using the method of gravity plate. The concentrations and their changes of marine and terrigenous air-borne microbial counts in the areas monitored were compared. The spatial and temporal distributions and the changing tendency of the air-borne microbial concentrations were analysed. The conditions of air borne microbes over the sea and land areas, the indoor and outdoor status of it, and the effects of human activity and environmental pollution on them were reflected.