The present study was planned to investigate the histopathological effects of the chitin synthesis inhibitor chlorfluazuron against the 4^th larval instar of Tribolium castaneum (Coleoptera: Tenebrionidae) under electron microscope level. Toxicity of chlorfluazuron was evaluated under three different temperatures. The sublethal concentrations LC₄₀ were 2.118, 39.76 and 1.207 ppm, at 20, 29 and 38^◦C respectively. Toxicity of this compound increased at relatively high temperature.  Ultrastructural studies were carried out on the integument of the prepupae treated as larvae with LC₄₀ of chlorfluazuron. The treated samples revealed that exuviae of the old cuticle were existed above the new formed integument, some densely–stained material was deposited in endocuticle, procuticle lamellae were disorganized and partially degenerated. Disappearance of moulting fluid. The hypodermis was destructed and detached from endocuticle. Mitochondria were swollen and fusion. Lysis of lysosomelike bodies.