By employing upper and lower solutions method together with maximal principle, we establish a necessary and sufficient condition for the existence of pseudo-C3[0,1] as well as C2[0,1] positive solutions for fourth-order singular p-Laplacian differential equations with integral boundary conditions. Our nonlinearity f may be singular at t=0, t=1, and u=0. The dual results for the other integral boundary condition are also given.