In this study, CuInS2 nanoparticles have been synthesized via one-pot facile thermolysis route and the decomposition temperature of CuCl and InCl3 complexes were investigated. The stabled colloidal CuInS2 compound has been prepared by solving CuCl and In2(SO4)3 as cationic elements, thiourea (SC(NH2)2) as sulfur source and PVP as surfactant in the nontoxic and cost effective solvent of Diethylene glycol ((CH2CH2OH)2O) and ethylene diamine(C2H8N2) . The samples were characterized by X-ray diffraction for structural evauation, Fourier transform infrared (FTIR) for revealing the formed complexes and capping agents and absorbance spectrophotometer (UV-VIS) for detecting optical properties. The results revealed that the In2(SO4)3 was decomposed when the temperature was more than 210oC and CuInS2 compounds with polytypism crystalline structure (chalcopyrite and wurtzite) was formed. Furthermore, increasing the temperature from 120 °C to 240 °C, facilitates formation of the chalcopyrite crystalline structure rather than the wurtzite structure.