The bagworm Acanthoecia larminati Heylaerts, 1904 (Lepidoptera: Psychidae) is reported for the first time damaging chestnut trees (Castanea mollissima, Castanopsis boisii and Lithocarpus bacgiangensis) in plantations in Vietnam. Field surveys revealed that C. mollissima trees were severely damaged by A. larminati. The damage incidence (P%) and damage index (DI) in C. mollissima plantations in Dien Bien, Lao Cai, Cao Bang, Bac Kan, Lang Son, Hoa Binh, Thanh Hoa and Kon Tum provinces were 20.2–81.6% and 0.36–2.74, respectively. The C. mollissima trees in Dien Bien, Hoa Binh and Thanh Hoa provinces were more severely damaged than in the other locations. Damage from this pest in C. boisii and L. bacgiangensis plantations in Lang Son, Bac Giang and Hoa Binh provinces was lower, with P% being 11.8–17.5% and DI being 0.13–0.27. Further research is needed to monitor outbreaks, identify biological and ecological characteristics, and develop control solutions for managing this pest.