Abstract-The Orthant-Wise Limited-memory QuasiNewton method (OWL-QN), based on the L-BFGS method, is an effective algorithm for solving the '1-regularized sparse learning problem. In order to deal with the '1-regularization, OWL-QN restrict the point to an orthant on which the quadratic model is valid and differentiable. In this paper, we propose an Inexact Orthant-Wise Limited-memory Quasi-Newton method (IOWL-QN). This method, at every iteration, compute an approximate solution satisfied the inexactness conditions to estimate the exact solution. We give brief proof to the convergence and report the numerical results.