Abstract: Kaolin filled ultra high molecular weight polyethylene (UHMWPE) based composites (coded as UHMWPE/Kaolin) were prepared by polymerization filling and melt mixing, respectively. The friction and wear properties of the composites under dry sliding against AISI 1045 steel were evaluated with an MM 200 friction and wear tester. The morphologies of the worn composite surfaces and of the transfer films on the counterface steel were observed by means of scanning electron microscopy (SEM) and stereo optical microscopy. As the results, kaolin at a certain content is very effective to reduce the friction and wear of UHMWPE. UHMWPE/Kaolin composites prepared by polymerization filling are superior to the ones prepared by melt mixing with the same filler content in terms of friction reduction and reducing wear. The differences in the transfer film characteristics and the structure of UHMWPE account for the different friction and wear properties of the two kind composites.