The experiments are done for the buckling load and the growth characteristics of graphite/epoxy unidirectional specimens with through-the-width delamination. The influence of geometric configurations, that is, the length and the thickness of upper part of delamination, on the buckling of beam-plate is considered by means of the six different specimens with various delamination configuration and one perfect specimen. Experimental results show good agreement with analytical solutions in the associated paper. In the postbuckling state, the buckling mode and the growth characteristics depending on delamination configuration are also discussed.