We establish a criterion for a set of eigenfunctions of the onedimensional Schrödinger operator with distributional potentials and boundary conditions containing the eigenvalue parameter to be a Riesz basis for L 2 (0, π).2010 Mathematics Subject Classification. 42C15, 42C30, 15B05, 34B07, 34L10, 34L40, 46B15, 46C05, 46E30, 47A20, 47B25, 47E05.Key words and phrases. Riesz basis, one-dimensional Schrödinger equation, distributional potential, Sturm-Liouville operator, singular potential, boundary conditions dependent on the eigenvalue parameter.