Systematic measurements of density were performed in six binary mixtures of carboxylic acids. Derived from the densities the excess molar volumes VE are always positive, with the exception of the formic acid+acetic acid system where VE is negative for x<0.75 and positive for mixtures rich in formic acid. The extremal values of VE are about -0.06 and +0.02 cm2 mol-1. As a rule, the excess molar volume curves are slightly asymmetrical with respect to composition having the maximal values of about 0.15 cm3 mol-1 in the formic acid+propionic acid system; 0.10 cm3 mol-1 in the acetic acid+ propionic acid system; 0.35 cm3 mol-1 in the acetic acid+n-pentanoic acid system; 0.65 and 0.62 cm3 mol-1 in the systems of n-pentanoic and iso-pentanoic acids with formic acid. A qualitative interpretation of the presented results is given taking into account almost complete dimerization of carboxylic acids and the formation of mixed dimers of these acids.