Polyethylene terephthalate (PET)/biomedical polyurethane (BPU) composite nanofibers with modulated mechanical properties are electrospun by varying the weight ratios of PET and BPU polymers in the mixture. The effect of BPU content on the morphology, porosity, thermal properties, and crystalline structures are systematically investigated. It is shown that uniform PET/BPU nanofibers can be formed through optimization. When the content of BPU is low (0-7 %), better elongation of the nanofibrous mats is obtained with the increase of BPU content, whereas further increasing the BPU polymer (up to 15 %) results in a decreased breaking elongation as well as the mechanical strength of composites. The formed nanofibrous mats may find potential applications in tissue engineering and vascular graft.