Carbon steel was exposed at atmospheric testing sites all over Vietnam in the period 1995–2000. The corrosion rate was determined by the weight loss method. The environmental data were collected at the same time of the exposures. The effects of the environmental factors on the corrosion of carbon steel were investigated. It showed that the corrosion rate increases with increasing relative humidity, TOW, chloride concentration in the air and decreasing air temperature. Based on the data of observed corrosion and the environmental factors the linear regression equation of one-year corrosion is given for carbon steel in coastal and continental area.