The influence of three cold flow improvers, namely, olefin-ester copolymers (OECP), ethylene vinyl acetate copolymer (EACP) and polymethyl acrylate (PMA), on the low-temperature properties and viscosity temperature characteristics of a soybean biodiesel was evaluated on a low-temperature flow tester and a rotatory rheometer. The crystal morphologies of the biodiesel at low temperatures were investigated through a polarizing microscope. The results indicated that the ability of the cold flow improvers differed in improving the cold flow properties of soybean biodiesel, of which OECP was the best candidate. OECP can significantly reduce pour point (PP) and cold filter plugging point (CFPP) of biodiesel and retard viscosity increase of biodiesel at low temperatures when incorporated into biodiesel at the additive contents of 0.03%. On the other hand, OECP functioned by inhibiting the wax crystals from growing to a larger size and provided a barrier to crystal agglomeration at low temperatures, thus improving the cold flow properties of soybean biodiesel. (C) 2010 Elsevier Ltd. All rights reserved.