A soybean biodiesel was prepared and blended with a conventional China's No. 0 petrodiesel. The pour points (PP) and cold filter plugging points (CFPP) of the biodiesel blends were evaluated on a low-temperature flow tester. Dynamic viscosities of the blends at different temperatures and different shear rates were measured on a rotatory rheometer. The crystal morphologies of the biodiesel blends at low temperatures were analyzed using a polarizing microscope. The results indicate that the blended fuels provided a slight decrease in PPs and CFPPs as compared with those of neat soybean biodiesel and pure petrodiesel. Below the temperatures of PPs or CFPPs, the dynamic viscosity of the biodiesel blends increased dramatically with decreasing temperature, but decreased with increasing shear rate, the biodiesel blends exhibiting non-Newtonian behavior. At temperatures higher than PPs or CFPPs, linear relationships appeared between dynamic viscosity and shear rate and the biodiesel blends became Newtonians. At low temperatures, wax crystals of the biodiesel blends grew and agglomerated rapidly. The loss of fluidity at low temperatures for the biodiesel blends can therefore be attributed, on the one hand, to the sharp increase of viscosity and, on the other hand, to the rapid growth and agglomeration of wax crystals.