The objective of the research study was to comparatively assess the sorption properties of comminuted grains of three quinoa varieties: red (I), white (II), and black (III). Under the research study, the water content and water activity were determined in the comminuted grains  and the vapour sorption isotherms were delineated with the use of a statistical method within the a_w = 0.07 ÷ 0.93 range of water activity. Also, the plotted isotherms were described mathematically using the BET, GAB, and Oswin and Peleg models. The parameters of  the two theoretical models (BET and GAB) were applied to estimate the monolayer capacity and specific surface area of sorption, while the  GAB model was also applied to estimate the total capacity of capillaries and the radius of capillaries subject to filling upon initiation of  the capillary condensation phenomenon. In order to estimate the parameters of the models tested, a non-linear regression method and a  Monte Carlo algorithm were applied. The minimization of the sum of residual squares was the goal function. The results achieved led to  the conclusion that the grains of the quinoa varieties studied differed in the initial water content and water activity as well as in the  sorption properties. The comparison of the sorption properties made it possible to show that the grains of black quinoa (III) was characterized by a better quality expressed as storage stability contingent on a significant development of the monolayer that protects  the product against unfavourable changes related to an increase in the amount of free water throughout the product storage life. The  quinoa variety-depending properties of its grains result in the differentiation of its sorption properties. In addition, the RMS value was  lower than 10 %; thus, on this basis it was confirmed that the GAB and Peleg models were those to best describe the sorption properties of  the grains studied.