The physical properties of ultrahigh molecular weight polyethylene (UHMWPE) are generally highly dependent on its molecular weight. However, in our study, it was found that two UHMWPE samples of similar molecular weight, SLL-5 and GUR 4150, have significantly different impact strengths, with the Charpy impact strength of GUR 4150 being almost 3.4 times that of SLL-5. To reveal the reasons, the structure-property relations of these UHMWPE materials were investigated. Morphologies of the nascent particles and impact fracture surfaces, the melting behavior, rheological behavior, and three-phase (crystalline, amorphous, and interphase) contents were characterized by scanning electron microscopy, differential scanning calorimetry, advanced rotary rheometer, and Raman spectroscopy, respectively. It was observed that no significant differences in the crystal structures of SLL-5 and GUR 4150, but GUR 4150 had smaller nascent particles sizes and a lower degree of entanglement when compared with those of SLL-5. Accordingly, a mechanism to clarify the significant difference in the impact strengths of GUR 4150 and SLL-5 was developed. More importantly, this work may be useful for improving the preparation technologies and industrial applications of UHMWPE. (c) 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 632-641