Pentachlorobenzene (PeCB) is Persistent Organic Pollutants, which can be formed and emitted unintentionally from anthropogenic source such as waste incinerators and the metallurgical industry. The decomposition mechanism of PeCB under different combustion temperature (200oC, 250oC, 300oC, 350oC, 400oC and 500oC) and different initial concentration of PeCB were investigated. The decomposition of PeCB concentration and other products were analyzed by gas chromatography - Electron Capture Detector (GC/ECD). The results showed that tetrachlorobenzene (TeCB), trichlorobenzene (TrCB) and dichlorobenzene (DCB) was the decomposition products. The results indicated that 1,4-dichlorobenzene + 1,3 dichlorobenzeneis the finial decomposition products. The results also showed that at dechlorinated products was about 83% at 500oC. Dichlorobenzene yield of PeCB with concentration of 4 mol/L (47.8%) was higher than that of 20 mol/L (33%) and 40 mol/L (18%). Keywords: decomposition, pentachlorobenzene, temperature