The paper presents the results of a research on determining the temperature and shearing rate effect on dynamic viscosity of type B biofuels. This type of fuels are diesel fuels containing a biocomponent supplement. The “B” value denotes a volumetric share of the biocomponent in a mixture with diesel fuel. Three kinds of biofuels have been tested: B100 (100% RME), B20 (20% RME) and B5 (5%RME). B20 and B5 biofuels were prepared on the basis of commercial VERVA ON diesel oil. The dynamic viscosity of B100 RME biofuels within the temperature range from 30 to –15oC assumes values from c.a. 10 to 95 mPa·s. The dynamic viscosity of RME biofuels at constant temperature 25oC within the range of shearing rate from 0 to 2000 s–1 changed its value from 7 to 15 mPa·s. B5 biofuel reveals also a strong dependency of the dynamic viscosity in the shearing rate function. For the lowest values of the shearing forces the dynamic viscosity assumed the values of 2.5 mPa·s. The dynamic viscosity grew reaching the value of 8.5 mPa·s at 2000 s–1 along with the increasing shearing forces. The research demonstrated that the dynamic viscosity of fuels is seriously affected not only by the temperature, as has been hitherto suggested, but also by the shearing rate.