The eigenvalue and the inverse eigenvalue problems of the Sturm-Liouville operators defined respectively on[0,1][0,t0 ]and [t0 ,1]are considered.By using the monotonicity of the Weyl-Titchmarsh-m-function,it is shown that the three spectra are alternate,and the potential q (x)and the parameters h,H in the boundary conditions can be uniquely determined by the three spectra if the spectra of the operators defined on subintervals are disjoint.