Self-crosslinkable lignin/epoxidized natural rubber composites (SLEs) were prepared through a high-temperature dynamic heat treatment procedure followed by a postcuring process. Because of the ring-opening reaction between lignin and epoxidized natural rubber (ENR), lignin as a crosslinker and reinforcing filler was uniformly dispersed into the ENR matrix and was highly compatible with the polymer matrix; this was confirmed by scanning electron microscopy. The curing behavior, mechanical properties, and dynamic mechanical properties of the SLEs were studied. The results show that the crosslinking degree, glass-transition temperature, modulus, and tensile properties of the SLEs substantially increased with the addition of lignin. A physical model was used to verify the strong interactions between lignin and ENR. Stress–strain curves and X-ray diffraction suggested that the reinforcement effect on the SLEs mainly originated from lignin itself rather than from strain-induced crystallization. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41166.