The in-situ composites of polyamide 6 (PA 6)/liquid crystalline polymer (LCP) were investigated from the standpoint of fibrillation of LCP to develop a new high performance gear material for heavy load use that is superior to conventional plastic gears made of polyacetal (POM). LCP used was a wholly aromatic copolyester. PA 6 was chosen as the matrix polymer because of its excellent fatigue resistance. Extrusion of PA 6 added with LCP from 10 to 30 vol% was carried out at a temperature between 260 and 290 degrees C by a twin screw extruder and take-up equipment. In-situ fibrillation of LCP droplets, which were dispersed in PA 6 matrix, took place during the process. Injection molding of the composites was followed at a temperature below the softening point of LCP fibrils so as to keep the fibrils as extruded. Key factors for fibrillation of LCP were found as follows: 1) control of stress relaxation of LCP when the melt passes through the die-head, 2) the optimum temperature of melt, 3) the optimum LCP content, and 4) addition of a small amount of 3rd component. A gear made of in-situ composite of PA 6/LCP (30 vol%) added with 2-functional epoxy resin (2.5 phr) was found to bear a load about 1.2 times heavier than a POM gear.