The power generation sector contributes directly to SO2 emissions, causing economic and environmental damage. These SO2 emissions come mostly from the,combustion of fossil fuels for power generation. A multiperiod mixed-integer nonlinear model for power generation planning with SO2 consideration is presented in this paper. The objective of the model is to determine the optimal mix of energy supply sources and SO2 emission mitigation options that meet a specified electricity demand and SO2 emission targets at minimum cost. The model is written in a general format and it is illustrated in a case study from Ontario Power Generaton (OPG), Canada. SO2 emission's from power generation can be reduced through fuel balancing (which is simply to increase production from non-fossil-fuel power plants and decrease production from fossil-fuel power plants), fuel substitution or the use of low sulfur fuels, and conventional flue gas desulfurization. These options were considered in the model and the results, for the case study, show that if no SO2 emissions reduction target is imposed, the model does not tend to apply any of the options considered. However, the model recommends building more power plants to meet the electricity demand for the coming 10 years. The electricity cost increases to similar to 8.2 cents/kWh in year 2017. For another case study in which different SO2 reduction targets are considered, the model shows that fuel balancing and fuel switching must be applied immediately in several plants.