This paper reports the effects of spent polyethylene (PE) addition on the bituminized waste forms with ash. In addition, leaching mechanism of those waste forms is evaluated through leach testing. The additive used for the experiment was spent PE generated from an agricultural polyethylene film. The bitumen used in sample preparation was straight-run distillation bitumen, a paving asphalt. The waste used for the experiment was a bottom ash generated from a hazardous wastes incinerator. Bituminized waste forms with PE contacts of 5 wt% or more resulted in maintaining dimensional and mechanical stability. The compressive strength and softening point of bituminized waste forms are found to increase in proportion to the amount of spent PE. Leach testing also revealed that the principal leaching mechanism of metals (Cd, Cr, Cu, Pb) from bituminized waste forms is diffusion. Furthermore, it is demonstrated that additive PE of 5-10 wt% does not change leaching mechanism, and bituminized waste forms maintain a high leach resistance.