Assuming the degradation of styrene-butadiene rubber (SBR) during its practical usage, the accelerated weathering tests were conducted with various pre-strains. Although the isotropic narrower cracks form under no pre-strain (0% strain), the wider crazes orients perpendicular to the pre-strained direction under 20% pre-strain. The larger prestrain of 40% induces the vertical penetration of these crazes vertically from the exposed surface. The cross-sectional observation under 80% pre-strain suggests that the further craze propagation finally tears the sample inside. Correspondingly, both of breaking strength and strain significantly decreased with increasing pre-strain. In contrast, the post-strain applied after the accelerated weathering test under no pre-strain gave only the middle cracks, suggesting that the initial narrower cracks grow into the latter wider crazes during the accelerated weathering tests under prestrained. The origin of such initial narrower cracks is attributable to the pre-strained structure before the accelerated weathering test, which was confined by scanning probe microscopy (SPM) observation. The distribution of carbon black (CB) mixed in the base rubber was biased even at the low strain. The characteristic phase separation of CB domains gave the narrower cracks during the accelerated weathering test, which further grow into the wider crazes and inside tearing.