Corrosion occurred on steel bridges which were constructed in mountainous area. However, few studies have investigated the corrosive environment of steel bridge in mountainous area. In this research, Temperature, humidity, wind conditions and amount of airborne salt have been observed at bridge site. In order to comprehensively assess corrosive condition, exposure test was also performed. Observation and exposure test were conducted at the steel plate girder bridge with 60m length and three main girders. During observation period, anti-freezing agent (Na-Cl) is sprayed in winter. From the observation, time of wet on the bridge is longer than bridges those were constructed at coastal area. It was clearly observed that flying behavior of anti-freezing agent around superstructures is influenced by the prevailing wind. Furthermore, distribution of amount of adhesion salt at the surface of steel in the bridge section was also clarified. Rust thickness of exposure specimen was revealed that the influence of anti-freezing agent, and at lower flanges becomes larger than that of web. These results can be applied to corrosive environmental simulation of steel bridges.