Sclerostin is an extracellular negative regulator of bone formation that is a recognized therapeutic target for osteoporosis therapy. In the present study, we performed DNA aptamer selection against sclerostin, then characterized aptamer-sclerostin binding and the ability to inhibit sclerostin function in cell culture. We show that a selected DNA aptamer was highly selective for binding to sclerostin with affinities in the nanomolar range as determined by solid-phase assays and by isothermal titration calorimetry. Binding between sclerostin and the aptamer was exothermic and enthalpically driven. CD confirmed that the aptamer had temperature-dependent parallel G-quadruplex characteristics. The aptamer was stabilized with 3' inverted thymidine to investigate efficacy at inhibiting sclerostin function in cell culture. The stabilized DNA aptamer showed potent and specific dose-dependent inhibition of sclerostin's antagonistic effect on Wnt activity using a reporter assay. Taken together, the present findings suggest an alternative approach to inhibiting sclerostin function with therapeutic potential.