Smear wear behavior has often been observed during rubber abrasion, especially under mild test severities. It generates degraded sticky rubber debris that often produces erratic measurements of abrasion weight loss. Various practical methods to avoid or remove the debris from the abrasion test surface have been reported, such as applying a drying powder lubricant. However, the detailed mechanism of smear wear behavior is still not clear. Various characterization techniques are applied to investigate the smear wear of both an unfilled NR model compound and a commercial carbon black (CB)–filled SBR tire tread compound obtained during blade abrasion testing. The debris showed lower molecular weight and higher oxygen content than the virgin materials. In addition, 75% of the smear wear was found to be de-crosslinked during smear wear, as detected by the double quantum-NMR technique. For the first time, it is demonstrated that both the polymer itself and crosslinking points are broken down during smear wear. The effect of the smear layer on friction and abrasion is also discussed.