Electrolytic conductivity often is used at the present time to measure the SO2 in the air. The error factor in the electrolytic conductivity method is greatly affected by a positive offset based on the evaporation loss of the absorbed liquid when pollutants are other than SO2. However, the establishment of a logical air pollution prevention measure makes it desirable to design a reliable automatic measuring instrument with SO2 selectivity. This report concerns a flame photometric detector (FPD) method with SO2 selectivity. Listed are the results of a comparison made between performance tests using standard gas, and the rosaniline method used in field tests. It is believed that the measurement of SO2 by the FPD method can be used in practical applications.