Municipal Solid Waste Incinerator (below MSWI) ash is used to develop inorganic binder for preparing geopolymer concrete in this study. Toxic substituents, such as heavy metals are de-toxificated by above-mentioned new solidity technique. Slag and coal fly ash are used as active filler to enhance compressive strength. MSWI ash was mixed with slag and coal fly ash to make geopolymer concrete. They were solidified under alkali condition and dried at 50°C and 80°C, respectively. Compressive strength was measured to evaluate the characteristics of specimens for the period of 3, 7 and 14 days. Compressive strength measurements show a maximum strength of almost 13.7 MPa after 14 days. The mineral phases of specimen were analyzed by XRD. And the morphology was analyzed by the photo of SEM. The micro-structure of inorganic binder prepared was analyzed by FTIR. Korea Standard leaching Test (KSLT) and TCLP method are used to the environmental safety of inorganic binder. Raw FA measured concentrations of Cu and Pb were 0.30 ppm and 28.31 ppm, respectively. Leaching amounts of heavy metal were noticeably reduced after the solidification of MSWI as with active filler. It is possible to de-toxificate MSWI ash by new solidity techniques. And it may be used as alternative concrete.