We report the first Raman study of GaAs-Al 0.5Ga 0.5As-AlAs polytype superlattices grown by molecular-beam epitaxy. Folded longitudinal acoustic phonon modes were observed for all the samples. The frequencies agree well with those calculated using an elastic continuum model. The intensities of the folded modes have novel properties, compared with double-constituent superlattices like GaAs-(AlGa)As.