In this paper, we prove the applicability of the strong stability method to inventory models. Real life inventory problems are often very complicated and they are resolved only through approximations. Therefore, it is very important to justify these approximations and to estimate the resultant error. We study the strong stability in a periodic review inventory model with an (R,s,S) policy. After showing the strong v-stability of the underlying Markov chain with respect to the perturbation of the demand distribution, we obtain quantitative stability estimates with an exact computation of constants.