The problems of leachate treatment and landfill gas (LFG) emissions are increasing gradually. Reducing the hazard before emplacement, pretreatment of municipal solid waste (MSW) prior to landfilling has become very important for the conventional landfill. In this study, pretreated mixed un-shredded MSW by the natural convection of air was employed to assess the aerobic pretreatment suitability. To study the effects of pretreated waste on landfill behavior, landfill simulation reactor (LSR) was developed at laboratory scale; pretreated MSW was placed in it. In a LSR, the behavior of aerobically pretreated waste disposal on a landfill was simulated. The LSR was operated for more than 9 months. The LSR operating phases were analyzed together with the consolidation of the leachate and gas production. The leachate collected was analyzed for pH, BOD (biochemical oxygen demand), COD (chemical oxygen demand), NH3-N and trace metals. The gas collected was analyzed for CH4 and CO2. The COD and BOD values were reduced to 1850 mg/L and 235 mg/L respectively within 5 months respectively. The maximum landfill gas (LFG) generation was observed about 60 m3 per ton dry matter (DM) of MSW. This work demonstrates that pretreatment is significantly effective in reducing the landfill emissions that is LFG; and leachate quality was improved in terms of COD and BOD.