We consider in \(L_2(\mathbb {R})\) an elliptic second-order differential operator \(A_{\varepsilon }\) , \(\varepsilon >0\) , given by \(A_{\varepsilon } = - \frac{d}{dx} g(x/\varepsilon ) \frac{d}{dx} + \varepsilon ^{-2} p({x}/\varepsilon )\) , with periodic coefficients. For small \(\varepsilon \) , we study the behavior of the resolvent of \(A_{\varepsilon }\) at a regular point close to the edge of a spectral gap. We obtain an approximation of this resolvent in the “energy” norm with an error \(O(\varepsilon )\) . The approximation is described in terms of the spectral characteristics of the operator at the edge of the gap. Bibliography: 22 titles.