The current study was carried out to establish the appropriate environmental sphere of application for unpainted weathering steel as civil structures, such as bridge structures, general construction, electric posts, guide rails, etc. As such, based on existing guideline for acceptable flying marine salt concentrations, the suitability of 4 selected locations was investigated in relation to environmental factors, including the direction and velocity of the wind, rainfall, humidity, and temperature. The results for the flying marine salt concentrations, considering the character of the selected locations, were as follows: the maximum and minimum flying marine salt concentrations measured by the gauge method at the selected locations #1, #2, #3, and #4 were 0.046 and 0.094, 0.08 and 0.131, 0.050 and 0.08, and 0.021 and 0.051 mg-NaCl/dm(2)/day, respectively. The concentrations of flying marine salt at locations #3 and #4 were lower than 0.1 mg-NaCl/dm(2)/day, indicating that the application of unpainted weathering steel was possible in these positions. However, the maximum concentration of flying marine salt at location #2 was 0.131 mg-NaCl/dm(2)/day. Accordingly, the current results revealed that locations #3, and #4, which were farther than 1000 m from the sea coast, were appropriate environments for the use of unpainted weathering steel, whereas location #2, which was less than 1000 m from the sea coast was found to be an unsafe environment for the use of unpainted weathering steel.