The specific position of a group in the molecule has been considered and a group vector space method for estimating the critical properties of organic compounds developed. Expressions for estimating the critical properties T-c, P-c, and V-c of organic compounds have been proposed and the numerical values of relative group parameters presented. The average percent deviations of estimation of the above three properties are 0.69, 2.15, and 1.43, respectively, which show that the present method demonstrates significant improvements in accuracy and applicability, compared to the conventional group methods.