The structural change in phase transition of hybrid(C12H25NH3)2MnCl4 was investigated.The temperature and the structures of the phase transition is investigated by thermal gravimetry(TG)and differential scanning calorimetry(DSC),infrared spectrum(IR)and X-ray diffraction(XRD).The results suggest that the phase transition is reversible and the structural change arises from the conformation change of the organic chain.The interlayer distance increases when the hybrid transforms from low temperature phase to high temperature phase.This is explained by the diffusion of gauche-bond along the organic chains and they move away from each other when the phase transition occurs.Combining the experimental data with theoretical calculation,we propose that organic chain of the hybrid in high temperature phase is the conformation of gauche-bond altating with trans bond(noted as GTG’TGTG’TGTG’T).