The paper presents new data on the orchid diversity in Vietnam obtained in 2016–2020. It contains descriptions of one genus (Apetalanthe) and two species new to science (Apetalanthe gracilis, Nervilia appressifolia), as well as one genus (Neottianthe) and four species (Calanthe tricarinata, Collabium yunnanense, Dendrobium praecinctum, Neottianthe secundiflora) new for the flora of Vietnam. Apetalanthe is particularly remarkable for the reduction of petals. The accepted name, synonyms, type, citations of relevant regional taxonomic publications, data on ecology, phenology and distribution, estimated IUCN Red List status, studied specimens, brief taxonomic notes, and illustrations are provided for each recorded species.