Abstract: The research focuses on the solidification/stabilization of heavy metal contaminated landfill Decomposed Solid Waste (DSW). DSW samples were collected from Matuail and Aminbazar landfill sites of Dhaka South City Corporation and Dhaka North City Corporation respectively. Ordinary Portland Cement (OPC) was used as stabilizing binder to investigate the feasibility of solidifying/stabilizing the waste. A series of trials were observed for optimum composition of OPC and fine aggregate in mortar mixture. Solid waste was mixed as the substitute of total volume of fine aggregate as big as 10-70%, with the range of 10% per composition. The study observed the strength development and immobilization of heavy metals like Fe, Cu and Ni of the final product. This study revealed that 30% of the total volume of the fine aggregate can be replaced by dry decomposed solid waste having a mix proportion 1:3 of stabilizing binder (i.e., OPC) and fine aggregate which obtained compressive strength 2494 psi at 28 days curing period that satisfy the Bangladesh standard for paving block. Immobilization of Fe, Cu and Ni were obtained ranges from 96.5-95.0, 88.16-72.64 and 93.05-89.28%, respectively for different composition of solidified matrix. The Outcome of this study gives the information of compressive strength development of solidified waste mortar block and immobilization (i.e., entrap) of heavy metals within the block to minimize the release into the environment.