In this paper, we nd a new non-Riemannian quantity for (\alpha;\beta )-metrics that is closely related to the \tilde{S}-curvature. We call it the \tilde{S}-curvature. Then we show that an (\alpha;\beta )-metric is Riemannian if and only if \tilde{S}=0. For a Randers metric , we find the relation between S-curvature and \tilde{S}-curvature.
