Formaldehyde has been in widespread industrial use since World War II . Numerous sources of formaldehyde are present in the indoor environment. Additionally, the current trend toward tighter, more energy efficient buildings with lower ventilation rates has led to increase concentrations of this and other pollutants generated indoors. In this paper, the field survey was carried out once a month from January to MarctL 1994 to measure indoor and outdoor formaldehyde concentration in several underground locations in Seoul. The results could be summarized as follows : 1. At Yang- jae underground shopping center, the mean formaldehyde concentration was 77.8ppb for indoor and 68.4ppb for outdoor. At Ban- po underground shopping center, it was 175.8ppb for indoor and 127.3ppb for outdoor. At Jam- shil underground shop ping center, it was 135.2ppd for indoor and 34.6ppb for outdoor. Indoor the No.2 sub way line, it was 105.6ppb. The formaldehyde concentration using Berge equation was as follows : At Yang- jae underground shopping center, the mean formaldehyde concentration was 85.99ppb for indoor and 72.75ppb for outdoor At Ban- po underground shopping center, it was 254. 17ppb for indoor and 138.14ppb for outdoor. At Jam- shil underground shopping center, it was 249.13ppb for indoor and 36.87ppb for outdoor. Indoor the No.2 subway line, it was 131.73ppb. 3, The result of correlation analysis indicated that the relationship between temperature and formaldehyde concentration is very high( $gamma $= 0.831 ∼ 0.974). 4. Also, the relationship between humidity and formaldehyde concentration is variant ($gamma $ = 0.246 ∼0.999). 5. The mean formaldehyde concentration indoor and outdoor Ban- po underground shop ping center and indoor Jam- shil underground shopping center and indoor the No.2 sub way line exceed the American Society of Heating, Refrigeration, Air- conditioning Engineers( ASHRAE) stflndard of 100ppb(120 $mu $g/m$^{3}$).