Natural fiber reinforced biomass plastics (NFRPs) have been development because NFRPs are made from renewable resources and waste disposal of NFRPs is easy. Natural fibers have high specific modulus and strength, and thus natural NFRPs have a high potential for load-bearing materials. However, the dynamic and static fatigue strengths of natural fibers have been little understood. In this study, the time-dependent fracture of jute monofilaments was experimentally investigated and the fracture mechanism was discussed based on Zhurkov's model.