O.A.Veliev, M.Toppamuk Duman On the Sturm-Liouville Operator with Summable Potential (38K, LATeX 2e) ABSTRACT. We investigate the Sturm-Liouville operator \[ L(q)=-\frac{d^{2}}{dx^{2}}+q(x) \] in $L_{2}[0,1]$ with strongly regular boundary conditions and arbitrary Lebesque integrable Potential $q(x)$. We obtain asymptotic formulas of arbitrary order for eigenvalues and eigenfunctions of $L(q).$ Besides we give a simple proof of Riesz basisness of eigenfunctions and associeted functions of this operator.