Incineration of spent ion exchange resin was simulated using the ChemSheet chemical calculation program. The simulation of the incineration was modeled for typical spent resin produced by pressurized water reactors (PWRs) and boiling water reactors (BWRs) in Finland. The objective of the study was to find the volume and mass reduction and the chemical compounds formed during incineration. The simulation showed that active elements did not play any role in incineration owing to small amount of Cs, Co, etc. The ash contained metal oxides - mainly hematite, iron oxide Fe2O3. Other products of the incineration were water, carbon dioxide, sulfuric acid, and nitrogen oxides. The volume reductions 1/100 and 1/14 of the spent resin were obtained for PWRs and BWRs, respectively. The annual ash production from incineration was calculated to be 408 kg and 746 kg for the currently operating Finnish PWR and BWR plants in Loviisa and Olkiluoto, respectively.