Diffusion ordered NMR (DOSY) was applied to the determination of the average molecular weights of polymers based on the dependence of the measured self-diffusion coefficient D on the corresponding weights of a number of polymers of the same type. As a rule, a calibration function is plotted by varying DOSY experimental parameters for each particular test sample; however, this approach is inapplicable to the development of a standard procedure for the quantitative assessment of the molecular weights of dextrans. In this article, an optimization method is considered to ensure high resolution in terms of the values of D for dextrans without varying experimental conditions; this method makes it possible to evaluate the average molecular weights of dextrans with a high accuracy over a wide range of their values.