Polyamide 6/ZnO nanocomposites (noted as PA6/ZnO) were prepared by an in situ co-producing method, during which Zn-2(OH)(2)CO3 decomposed into nano-ZnO in the process of the opening-ring polymerization of caprolactam at high temperature. Transmission electron microscopy, X-ray diffraction, thermogravimetric analysis, and differential scanning calorimetry were used to analyze the size and dispersive properties of nano-ZnO, the crystallization and melting properties, the thermal properties, and crystal structure of PA6/ZnO composite, respectively. The results showed that the nano-ZnO derived from Zn-2(OH)(2)CO3 via in situ polymerization of PA6-ZnO was uniformly dispersed in PA6 matrix. However, the overall nano-ZnO crystallization rate and crystal size in the PA6 matrix were hindered by the bulky PA6 molecular chains. The mechanical properties were evaluated using universal tensile and impact testing instruments. The results revealed that PA6/ZnO composite with 0.2% nano-ZnO content possessed excellent tensile strength, enhanced by 75% in comparison with the pure PA6. The nano-ZnO had little influence on the impact strength of PA6. (c) 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 165-170