Abstract: Applying the generalized Leggett-Williams fixed-point theorem, the existence of positive solutions to the fourth-order boundary value problem is studied: u^\left( 4 \right)\left( t \right)=f\left( u\left( t \right) \right)\ \ \ \ \ \left( t\in \left 0, 1 \right \right), u\left( 0 \right)=u\left( 1 \right)=0, u''\left( 0 \right)=u''\left( 1 \right)=0, where f:\mathbbR\to \left 0, +\infty \right) is continuous. Under some conditions on f, there exist at least three symmetric positive solutions.