The theoretical part of the thesis: Physical properties of liquid fuels and bio diesel for combustion engines is aimed at describing the physical properties of fuels and ra-peseed oil methyl ester. It includes familiarization with the issue of dynamic viscosity and density of internal combustion engines and a comprehensive overview of methods of measuring these quantities . Experimental work is devoted to experimental measurement of the temperature de-pendence of the dynamic viscosity and density of selected diesel samples with different concentrations of rapeseed oil methyl ester. The measurement results were processed into tables containing diagrams .