Small diameter vascular grafts were fabricated from pure Polyurethane (PU) as well as PU reinforced with a tubular weft-knitted fabric. The tensile properties of the reinforced composite vascular grafts were compared with that of the tubular fabric itself and the pure PU vascular grafts. The elasticity and strength of the reinforced vascular grafts were improved compared with the tubular fabric. Strength of the reinforced vascular grafts was 5–10 times of the strength of the pure PU vascular grafts. Expanding the tubular fabric to increase the inner diameter of the reinforced vascular graft reduced the graft’s strength and initial modulus, but the difference was reduced as the PU content was increased. For grafts of the same inner diameter, increasing the PU content increased the thickness and strength of the graft wall, which led to a general increase in the strength and initial modulus of the composite vascular grafts.