The interfacial strength is the most important mechanical property among those of constituents in Polymer Matrix Composite: PMC. In this study, we conducted the tensile tests on Single Fiber Composite specimen and observed initiation of interfacial debonding at different loading rates. As a result, we recognized dependency of the interfacial strength on strain rates. According to the elasto-plastic analysis assuming that matrix's yield stress varies depending on strain rates, the stress distribution of the interface becomes close to the elastic analysis and it can be concluded that the dependency of interfacial strength on strain rates is caused by matrix's dependency on strain rates.