Tear toughness tests were performed for a 6 mm thick 6N01-T5 aluminum alloy plate joint by friction stir welding. Tear test specimens were collected in various ways so that the crack propagates through the selected local region of the weld, and by which, the relationship between the crack growth resistance and the local microstructure was examined. Morphology of the load-displacement curve and the obtained unit crack propagation energy (UEp) were systematically changed reflecting the local microstructural difference in the vicinity of the weld region. As for the as-weld condition, UEp of the weld region was larger than that of the T5 treated parent plate. For the middle of the weld region consisting of refined equiaxed grain structure (so called “stir zone”), UEp was larger than the surrounding outer region with a pancake-like grain structure. Specimen surface observation found that fine slip lines appeared when the crack propagated through the stir zone. In contrast, a rough and coarse slip pattern was dominant when the crack propagated through the outer region of the weld zone. The obtained load-displacement curve, UEp values and change in specimen surface appearance provided a quite reasonable correlation to the local microstructual characteristics in the weld zone.