Abstract: The polymorphism characteristics of p-tert-octyl phenol was studied.It was found that after thermal treatment of differential scanning calorimetry(DSC), the melting point of p-tert-octyl phenol sample was about 75.0℃,lower than that of the untreated original sample which was 85.4℃.The fusion enthalpy of p-tert-octyl phenol decreased with increasing cooling rate of the thermal treatment.The samples before and after the thermal treatment of DSC were analyzed with DSC, FTIR spectroscopy,and powder X-ray diffraction.The results showed that through the thermal treatment, p-tert-octyl phenol generated a new crystalline form with a lower melting point and lower fusion enthalpy.The solid stability of the polymorphs was further studied.It was found that the two polymorphs belonged to monotropy.The α form with a higher melting point was stable at temperatures below its melting point.The β form with a lower melting point was metastable, which could convert into the α form at a low temperature.