The behavior and characteristics of heavy metals at different streams in a MSWI(Municipal Solid Waste Incinerator) with a capacity of 100tonnes/day were investigated by measuring the concentration of heavy metals and gases and analyzing their leaching data from ashes. Metal components of Cr, Cu, Cd and Pb were in higher concentrations in the fly ashes collected after the water spray tower than in the bottom ashes. It was due to condensation by a lower temperature with water spray cooling. Metal contents in the bottom ash became higher for finer particles as expected. The mass balance of heavy metals in different stream was estimated from the analyzed data in bottom ash and collected dusts at different locations. For the lower volatility of metals such as Pb, Cu, Cr, 88-97% of them remained in the bottom ash, while Cd and Hg escaped from the combustor with remaining in bottom ash of 18.4 and 0.8%, respectively. In most cases the leaching rate of fly ash showed higher values than that of bottom ash, with the their average acidities of 9.8 and 11.9 respectively.