Flexible　multi-beam　structures　are　significant　components　of　large　space　station,　architecture　engineering　and　other　structural　systems.　The　understanding　of　the　dynamic　characteristics　of　these　structures　is　essential　for　their　design　and　control　of　vibrations.　In　this　paper,　the　planar　nonlinear　vibrations　and　chaotic　dynamics　of　an　L-shape　flexible　beam　structure　will　be　investigated　using　theoretical　and　experimental　methods.　The　L-shape　beam　structure　considered　here　is　composed　of　two　flexible　beams　with　right-angle.　The　governing　equations　of　motion　for　the　L-shape　beam　structure　are　established　firstly.　Then,　the　method　of　multiple　scales　is　utilized　to　obtain　a　four-dimensional　averaged　equation.　Numerical　method　is　used　to　analyze　the　nonlinear　dynamic　responses　and　chaotic　motions.　Finally,　The　experimental　apparatus　and　schemes　for　measuring　the　amplitude　of　nonlinear　vibrations　for　the　L-shape　beam　structure　are　introduced　briefly.　Then,　the　detailed　analysis　for　experimental　data　and　signals　which　represent　the　nonlinear　responses　of　the　beam　structure　are　given.　Copyright　©　2008　by　ASME.