This paper studies the existence of solutions for the fou rthorder boundary value problem u^(4)(t) = f(t,u(t),u″(t)), t∈[0,1],u(0)=u(1)=u″(0)=u″(1)=0,where f: [0,1]×R×R→R is a Carathéodory function. In the general case without restriction for growth condition of f and assumption of monotonicity on f, the author obtains the existence results of solution by using the met hod of lower and upper solutions. The validity of finding solutions with the mo notone iterative method is also discussed.