Pleated and flattened multiwalled carbon nanotubes are formed by the Fe-catalyzed thermal chemical vapor deposition with additive CaO: paisley-shaped pleats are shaped on one side of each bundle of flattened nanotubes. Transmission electron microscopy observations reveal that tetrahedron-like foldings are also formed in pleated nanotubes, suggesting a possible formation process that involves a kind of folding mechanism, the origami mechanism.