Mechanical reinforcement of silk membranes by embedding silk microfibers was studied. Silk microfibers of 10-600 mu m long were prepared by hydrolyzing degummed silk fibers in alkali solution. The silk microfibers were mixed with silk fibroin solution (continuous phase) at various ratios to fabricate silk microfiber-reinforced composite scaffolds (SMCSs). The morphology, mechanical properties, structural characteristics, biodegradation, and cytotoxicity of the composites were investigated. Silk microfiber-reinforced membranes with 1 wt% of microfibers displayed the most homogeneous distribution of microfibers in the membrane matrix. The tensile strength and elongation at break were 10.5 +/- A 2.7 MPa and 56.7 +/- A 7.8 %, respectively, comparable to human meniscus tissue. The presence of silk microfibers did not significantly impact the secondary structure and crystallization of SMCSs. Proteolytic degradation in vitro using protease XIV showed that the 1 % silk microfiber-reinforced membranes lost 90 % weight after 5 days, a longer time frame than plain silk membrane controls. The viability of human fibroblasts (Hs 865.Sk) on the SMCSs demonstrated no cytotoxicity. SMCSs may be useful as biomaterial systems as tissue substitutes where mechanical strength is critical for functional performance.