New taxonomic and distributional data are provided for three eastern Asian species of Calamagrostis (Poaceae, Agrostidinae) in Vietnam: C. abnormis (Hook. f.) Shukla, C. extremiorientalis (Tzvel.) Prob. and C. tripilifera Hook. f. The new national record of C. extremiorientalis is reported here for Vietnam, where it was previously misidentified as C. elatior (Griseb.) A. Camus or Deyeuxia petelotii Hitchc. (= C. abnormis). The presence of C. tripilifera and C. abnormis in Vietnam is confirmed. Additional new provincial records of C. extremiorientalis from Japan’s Bonin Islands (also known as the Ogasawara Islands) and C. tripilifera from Daba Mountains in the northern Chongqing Municipality (Central China) are reported here. A key for identification of Calamagrostis species in Vietnam, nomenclatural data and information about geographical, altitudinal and habitat distributions are provided. Maps showing their complete distribution in eastern Asia are presented.