This report deals with the large deformation of thin cantilever beams of nonlinear materials, subjected to a concentrated load at the free end. Because of the large deformations, both geometrical and material nonlinearities arise. Applications of the elastica theory have been confirmed to materials with linear stress-strain laws. In this report, the stress-strain relationships of the materials are represented by the Ludwick relation in considering the material nonlinearitiy. Theoretical analyses are compared with the experimental data. The agreement is found to be fairly close