The strain-induced crystallization of natural rubber (NR) was investigated by the measurement of the tear energy of a crosslinked blend consisting of NR and noncrystalline styrene-butadiene rubber (SBR). When NR was dispersed into the SBR matrix, the tear energy of SBR increased at various temperatures and tear rates. After the application of the principle of time-temperature superposition to the tear energy according to the Williams-Landel-Ferry equation, two distinct curves were found for the NR/ SBR blend with respect to the reduced tear rate, despite the fact that the tear energy of SBR or the SBR/SBR blend gave its own single composite curve. When the fatty acid in the NR/SBR blend was removed by acetone extraction, the tear energy of the blend drew a single composite curve. The conversion of the two curves into the single composite curve for the NR/SBR blend suggested that the tear energy depended on the strain-induced crystallization of NR dispersed in the SBR matrix, which was suppressed by the removal of the fatty acid. (c) 2005 Wiley Periodicals, Inc.