The interfacial properties and mechanical behavior of the SCS-6/Si3N4 composites fabricated by hot pressing from powder lay-up and tape lay-up techniques were studied. Interfacial shear strength and frictional stress were measured using an indentation test. Fracture toughness and work-of-fracture were measured using a three-point bending test on a chevron-notched specimen. The influence of interfacial shear strength on the toughening mechanisms and crack propagation behavior were investigated. The results indicate that the processing routes and fiber orientation will affect the interfacial properties, which in turn have a significant influence on mechanical properties.