The susceptibility effect of matrix material on g value of any radical has theoretically been investigated. An equation which yields the relationship between the g value of radical and the magnetic susceptibility of matrix material has been deduced. Based on this equation, it has been concluded that if the matrix material is paramagnetic the g value of the radical becomes smaller than the g value of the same radical in vacuum while it becomes higher if the matrix material is diamagnetic. These statements have been found to be in good agreement with the experimental results. (C) 2008 Elsevier B.V. All rights reserved.