The present invention relates to a method of refining crude tall oil. According to the method, the crude tall oil is fed into a column distiller, where it is separated into desired fractions. The conditions of the column distiller are adjusted on the basis of the composition of the feed and the product flow. According to the present invention, the densities of the crude tall oil fed into the column distiller and of at least one product flow are measured accurately as a function of the temperature. The density values are compared with correlation coefficients derived from the chemical compositions of the flows, coefficients which are obtained on the basis of laboratory analyses made earlier from corresponding flows, by using temperature compensation to specify the correlations, and by taking account of the regular variation in the wood composition of fresh wood according to the annual cycle and, as a result, the compositions of the flows are achieved. The present invention decreases the number of chemical analyses and improves the uniformity of the products.