Abstract
A new species, Onnia kesiya, is described from South Vietnam on the basis of morphological characteristics and molecular phylogenetic evidence. It is characterized by distinct lateral stipe, relatively thin and duplex context, hooked hymenial setae, widest basidiospores among Onnia species, and grows on Pinus kesiya in tropical pine forest. Detailed description with a photo and illustration is provided for the new species, and its relationships with similar species are discussed.