In this work, dispersion of sulfur dioxide (SO₂) in the vicinity of Mae Moh power plant, the largest fossil fuel power plant in northern Thailand, was investigated using well known air dispersion model. The area of 2,500 km² around the plant was studied, with spatial resolution of 200 x 200 m². Publicly available MM5 and CALMET software were used to provide meteorological conditions within the study domain, while CALPUFF was used to simulate the patterns of SO₂ dispersion, based on actual plant operations in winter, summer and rainy seasons of the year 2009. Comparison against measurements from monitoring stations was made. Simulated results were found to agree qualitatively and quantitatively well with measured data. Root mean squared errors were found in the range between 2.19 to 8.32 µg/m³. The CALPUFF model can be used for SO₂ dispersion prediction with satisfactory accuracy.