This study was carried out in order to produce bituminized waste forms, which have dimensional and mechanical stability like cement-based waste forms. This paper reports the effects of adding polyethylene (PE) to the bituminized waste form. The additive used for the experiment was the spent PE generated from agricultural use. The bitumen used in the sample preparation is straight-run distillation bitumen of penetration 60/70 (paving asphalt). The waste used for the experiment was a bottom ash generated from an industrial (inactive) waste incinerator. Bituminized waste forms with PE contents of 5 wt% or more resulted in maintaining dimensional and mechanical stability. The compressive strength and softening point of bituminized waste forms increase in proportion to the amount of additional PE. The leaching test using ANS 16.1 shows that the principal leaching mechanism of elements (Cs, Sr, Co) from bituminized waste forms is diffusion. Furthermore, it is demonstrated that additive PE of 5-10 wt% does not change the leaching mechanism, and bituminized waste forms maintain a high leach resistance.