Natural rubber (NR) composite elastomers have been increasingly explored recently, because they are renewable and environment-friendly. The excellent toughness of rubber composites is the premise to their wide applications. Unfortunately, an increase in tensile strength for NR is always accompanied by a decrease in extensibility. In this paper, an NR-based composite elastomer reinforced by triethoxyvinylsilane-modified leather collagen fibers (M-LCF) was fabricated for the first time to improve the tensile strength and the extensibility of the rubber composite simultaneously. The synergistic effect of the multiscale structure of M-LCF in toughening and its interfacial interaction with rubber promoted the dispersion of leather collagen fibers in the rubber and facilitated effective interfacial stress transfer, thereby enhancing the mechanical properties of the composite. The tensile strength, elongation, and toughness at the break of the composite elastomer containing 5%-modified collagen fibers reached 18.76 MPa, 740%, and 54.09 MJ.m(-3), respectively, which were 31%, 2%, and 64% higher than that of the pure rubber elastomer, respectively.