A series of poly(butylene terephthalate) (PBT) based composites with modified potassium titanate whiskers (MPTW) were prepared through in- situ polymerization. The surface properties and loading amount of MPTW were studied about their effects on the polymerization characteristics, microstructure, thermal stability, crystallization behavior, mechanical properties, friction- reduction, and wear- resistance of the PBT- based composites. The results show that the MPTW is in- situ chemical grafted with PBT, resulting in good dispersion and blurry phase interface. The in-situ grafted MPTW shows little effect on the thermal stability of PBT, but affects its semi-crystalline time. When the MPTW loading amount is 4%, mechanical properties of the composite reaches optimum, with a doubling of tensile strength and a tripling of impact strength compared to pure PBT. Additionally, the friction-reduction and wear-resistance of PBT are significantly improved with the addition of MPTW. Overall, the high- strength and wear- resistant PBT composites show potential application in the field of structural engineering plastic and mechanical transmission parts.