Monofilaments of in situ composites were prepared from an immiscible blend of a thermotropic liquid-crystalline polymer (TLCP), Rodrun LC3000, and a thermoplastic elastomer, styrene-(ethylene butylene)-styrene (SEBS), by a melt spinning process. Mechanical properties and the morphology of the composite monofilaments were investigated and compared with those of the extruded strands previously reported. The stresses at all tensile strains of the composite monofilaments were much higher than those of the extruded strands. The tensile strengths of both extruded strands and monofilaments were comparable, but the elongation at break of monofilaments dropped considerably. The tension sets of composite monofilaments were slightly higher than those of extruded strands. All composite monofilaments with TLCP content of less than or equal to15 wt % exhibited good elastic recovery under the applied strain up to 200%. The dynamic mechanical storage modulus at 25degreesC of 10 wt % TLCP composite monofilament increased fourfold compared with that of the composite extruded strand and fivefold compared with that of the neat SEBS monofilament. The dramatic enhancement in the mechanical properties of in situ composite monofilaments is due to the formation of finer and longer TLCP fibrils (length-to-width ratio >100) than those formed in the extruded strands. (C) 2003 Wiley Periodicals, Inc.