Abstract: The porosity change behaviors of municipal solid wastes (MSWs) are different from those of soils in the conventional soil mechanics, and they are influenced by both the solid mass loss due to biodegradation and the compression caused by surcharge load. Based on first-order kinetics, two different biodegradation models including single-component biodegradation model and multi-component biodegradation model are introduced for the modeling of solid mass loss in MSWs. Through the biodegradation model and a stress-age coupled compression model for MSWs, a porosity prediction model is presented. The change of porosity with time during biodegradation and long-term compression under different surcharge loads (10, 50, 100, 200, 400 and 800 kPa) is analyzed for different biodegradation models and MSWs with different compositions. For the current fresh MSWs in China, the porosity change behaviors predicted by means of the single-component biodegradation model and the multi-component biodegradation model are the same. It shows that the porosity increases with time during biodegradation under long-term compression. However, the porosity prediction model based on the multi-component biodegradation model can reflect the direct effect of waste composition and biodegradability on porosity change behaviors.