According to the measurements at Seoul Metro subway, the sound level at the time of subway arrival ranged from 77.0 to 92.5 dB(A). The highest level was 92.5 dB(A) at Line-1, and the lowest level was 77.0 dB(A) at Line-5. The sound level of departure ranged from the lowest level of 82.9 dB(A) at Line-5 and the highest level of 95 dB(A) at Line-1. The indoor sound level at subway ranged from the lowest level of 87.2 dB(A) (Line-6) to the highest value of 92.1 dB(A) (Line-1). The results of this study also showed that the sound level at subway platform with Platform Screen Door(PSD) showed 81.8 dB(A) but 89.1 dB(A) without PSD. The sound reduction effect of PSD showed 7.3 dB(A) at platform. Consequently, the sound level in Korean subway was found to exceed the standard set for the American Public Transportation Association (85dB(A)). Keywords : Subway noise level, Seoul, PSD, Railroad, Indoor, Line