Spatial distributions of gaseous pollutants CO, NOx, and SO2 in a street canyon in Fung-Shan, Kaohsiung County were measured. The street runs west-to-east with two lanes in a single direction: traffic flows only from west to east. The street canyon is 60 m long (= L) and 20 m wide (= W). The heights of the five-story buildings on both sides of the street are about 16 m (= H). Therefore, the street canyon has an aspect ratio AR (= H/W) = 0.8, and a length to width ratio L/H = 3. Air was sampled on site on three consecutive days, 3 September to 5 September, in 2003. The sampling period were 20 h long, from 00:00 to 19:00 on September 4, but covered only the two rush hours, 07:00-10:00 and 16:30-20:00, on the other two days. Traffic emissions were also estimated using available emission factors from TANEEB (1992). Results show that motorcycles are dominant vehicle in the street. Emission estimations indicate that motorcycle contributed to about 75% of CO emission, automobiles contributed about 80% of NOx emissions, while motorcycles and automobiles each contributed about 50% of SO2 emissions. Variations of traffic emissions generally follow traffic flow rates, indicating reasonable estimations of traffic emissions. When wind blows perpendicularly to the street canyon, air pollutants tend to accumulate in the leeward side. For example, concentration of CO in the leeward side is about two times that in the windward side. Generally, concentrations of air pollutants decrease with height, about 10% to 20% reduction in concentration, particularly noticeable in the leeward side. Results also show that, on leeward side, concentrations of air pollutants in the corridor were lower than those outside the corridor, being about 53.3% difference in CO concentration. However, on windward side, concentrations of air pollutants in the corridor were higher than those outside the corridor, being about 100% difference in NO2 concentration. Keywords: Street Canyon, Mobile Sources, Air Quality, Emission Factor.