This paper is concerned with the construction of a diffusion model for predicting SO₂ concentration in Tokushima prefecture. Firstly, the Fick's diffusion equation denoting SO₂ concentration is constructed where pollutant source intensities from stack emissions are estimated by fuel comsumption rate and sulpher content, and the diffusion parameters are determined by the method of least squares. Secondly, SO₂ concentration is predicted one hour in advance by applying estimation theory to the diffusion model. Simulation results indicate that the proposed method is effective for the prediction of SO₂ concentration.