Abstract: An annealing treatment was performed for polypropylene (PP) by using sodium phosphate as a nucleating agent, and the effects of annealing temperature and annealing time on mechanical performance, heat resistance, and crystalline properties of PP were investigated. The results indicated that the annealing treatment effectively improved the mechanical properties, heat resistance and crystallinity of PP. After being annealed at the temperature of 120 ℃ for 0.5 h, PP achieved an increase in tensile strength from 38.0 to 39.4 MPa, in flexural modulus from 1227 to 1882 MPa and in heat deflection temperature from 112.2 to 122.7 ℃. Moreover, the degree of crystallinity was improved from 36 % to 44 %.