The effeect of weld line on the morphology and mechanical properties of 70/30 polystyrene and polyamide-6 blends with various amounts of poly (styrene-co-maleic anhydride)(SMA) as compatibilizer was investigated. For blends without or with low content of SMA, the dispersed domains near the weld line were elongated parallel to the weld line; and the dispersed domains in weld line were spherical. But for blend with high content of SMA, the isotropic morphology was observed. And the dierence of morphology at weld line caused the distinction of fracture mechanism. The tensile strength of the blend is greatly influenced by the morphology of dispersed domains at weld line. While the morphology has only slight effect on impact strength of the blends.