A novel method, epoxidation/reduction of vegetable oils, is developed to prepare bio-based polyols for the manufacture of polyurethanes (PUs). These polyols are synthesized from castor oil (CO), epoxidized soybean oil, and epoxidized linseed oil and their molecular structures are characterized. They are used to prepare a variety of PUs, and their thermomechanical properties are compared to those of PU made with petroleum-based polyol (P-450). It is shown that PUs made with polyols from soybean and linseed oil exhibit higher glass transition temperatures, tensile strength, and Young's modulus and PU made with polyol from CO exhibits higher elongation at break and toughness than PU made with P-450. However, PU made with P-450 displays better thermal resistance because of tri-ester structure and terminal functional groups. The method provides a versatile way to prepare bio-polyols from vegetable oils, and it is expected to partially or completely replace petroleum-based polyols in PUs manufacture.