Relationship of corrosion rate of low carbon steel exposed to the open air and chemical and meteorological parameters including SO2, NOx suspended particulate matter, temperature, relative humidity, wind velocity, precipitation have been studied in Tokyo for these twenty years. In the late 1960s and early 1970s, the levels of SO2, SO42- and suspended particulate matter in the air were considerably high, but their levels had rapidly declined until the late 1970s. According to the trends of air pollution condition, corrosion rates of low carbon steel in the air have decreased in the same tendency. Yearly recent corrosion rates at Chiyoda, commercial and urban area were about 0.033mm/year, Funado, industrial area were about 0.04mm/year, Takao; rural and mountaneous area were 0.02-0.04mm/year, and Ichinose; mountaneous and remote area were 0.005-0.01mm/year respectively. Their difference of corrosion rates almost coincided with concentration of air pollutants, such as SO2, suspended particulate matter, NOx and sea salt. The relationship between corrosion rate and the air pollutant concentrations were confirmed by using statistical analysis of multiple regrresion and correlation. The most effective atmospheric factors to the corrosion rates were concentration of rain components such as H+, SO42-, NO3- and NH4+.