We propose Suzaku observations of two luminous low-mass X-ray binaries (Z sources), GX 349+2 and Cyg X-2, to investigate the origin of the hard tails of Z sources, of which the spectral photon indices are reported to become occasionally less than unity. With the high sensitivity of the HXD, we detect the spectral shape up to several 100 keV and reveal existence of particle acceleration caused by high radiation pressure.