Castanopsis megaphylla Hu, formerly recognized as endemic to China, is discoveredin Dien Bien province as a new record for the flora of Vietnam. Castanopsis megaphyllais morphologically similar to C. chevalieri Hickel & A. Camus and C. boisii Hickel&A. Camus, but differs from the former by much larger leaves, more pairs of secondary veins, a female flower per cupule, and from the latter by larger leaves, thicker infructescence rachis, bigger cupules and cupule completely covered by spines. Based on the collections from Vietnam, detailed description, illustration and photographs of C. megaphyllaare provided.