Here we describe and illustrate a new species, Melocalamus grandiauritus N.H. Xia, Q.M. Qin & J. B. Ni sp. nov., from the lowland forest in Thanh Hoa Province, Vietnam. Molecular phylogeny based on the GBSSI indicates that this species is a member of Melocalamus. Morphologically, M. grandiauritus is different from all congeneric species in Vietnam. It is somewhat similar to M. pacoensis H.N.Nguyen & V.T.Tran, but is easily distinguished by having much wider suborbicular culm leaf auricles, very high and ventricose auricles of foliage leaves, entire ligules of both culm leaves and foliage leaves, and large leaf blades.