Using the seamless specimen made of PMMA sheet by a vacuum-forming process at elevated temperature, an experimental investigation on tne buckling of imperfect truncated conical shells under axial compression is carried out. The imperfection implies here that the thickness of specimen is uniform in the circumferential direction and varies nearly linearly along its generating line. It is shown that the empirical formula given by WEINGARTEN et al. can be used conservatively in the design of imperfect truncated conical shells mentioned above representing their thickness by the mean value, and the initiation and propagation of buckling deformation are discussed. too.