In the present report, the low temperature flow characteristics of residual fuel oils by a Brookfield type rotary viscometer were studied and the following conclusions were obtained. (1) As the Brookfield type rotary viscometer can measure the viscosity of various liquids under varying rates of shear, it is very useful for estimation of flow characteristics of non-Newtonian residual fuel oils. (2) The increase in viscosity and non-Newtonian flow characteristic of residual fuel oils at low temperatures are caused by the wax contained in oils. (3) The pour point of residual fuel oil is one measure to estimated the low temperature fluidity but is not sufficient, it is therefore recommended to measure the low temperature viscosities of residual fuel oils by the Brookfield type rotary viscometer and to check the lowest temperature at which the residual fuel is used and also to determine the wax content in the residual fuel oils at -20°C.