The genus Cycas is revised for Vietnam. Twenty-four species are enumerated, nine of them described as new (C. aculeata, C. brachycantha, C. collina, C. condaoensis, C. pachypoda, C. dolichophylla, C. fugax, C. hoabinhensis, and C. tropophylla). Descriptions of two Chinese species known to occur close to the China-Vietnam border are also provided. A new combination is made for C. bifida (formerly C. rumphii var. bifida). The species are placed within an infrageneric classification previously outlined. Distribution of all taxa is mapped, and a key to species is provided. Illustrations are provided for new and poorly known taxa where adequate material has been available. Previous reports of C. circinalis and C. rumphii from Vietnam are discussed. Lectotypes are designated for C. balansae, C. chevalieri, and C. elongata, and a neotype is designated for C. pectinata.