This paper presents an analytical and experimental study conducted for postbuckling of I-section stiffeners. A stability analysis was carried out to determine postbuckling response of the stiffeners subjected to remote compression. The analysis is based on von Karman type plate equations and the minimization of the total potential energy of the deformation. An experimental program was conducted on I-section beams made from C3000/5225 graphite/epoxy woven cloth material. Buckling and postbuckling response were observed. The assumptions for boundary conditions along the junction of contiguous elements were checked by Shadow Moire tests. Preliminary results indicate that the load carrying capacity of the flange section is negligible in the postbuckling regime compared with that of the web section.