Municipal solid waste incineration (MSWI) bottom ash could be solidified with fly ash addition at 100 degrees C, and the flexural strength of solidified specimens reached almost 20 MPa. The strength development was found to be due mainly to C-S-H gel formation. Leaching tests were conducted to determine the amount of heavy metals dissolved from the solidified specimens, and the results showed that, under the hydrothermal conditions of this study, the leaching of heavy metals was very low. As such, it is possible to solidify MSWI ash by 100% (80% bottom ash + 20% fly ash) in a continuous production process with a low cost.