In this study, biodiesels were produced from canola and corn oil by using a methyl transesterification method. The viscosity values of canola and corn biodiesels and their blends were measured at the temperature range from 0 to 100 degrees C in the steps of 10 degrees C. In the same conditions, viscosities of diesel fuels were compared to viscosity values of biodiesels and the effects on viscosity of temperature were investigated. Viscosities of biodiesels are prominently decreased with increasing of their temperature, and thus, they are similar to diesel fuels in point of viscosity properties.