A new species of hover wasp, Eustenogaster nigra Saito and Nguyen, is described based on females and males collected mainly in northern Viet Nam. The wasp is also distributed in mountainous areas of central Viet Nam and the southern part of China. All distribution records are from areas with more-or-less distinct seasons in terms of temperature. The nest is described and compared with those of other Eustenogaster species. A nest collected during early spring in Tam Dao National Park in northern Viet Nam, where there is a more-or-less distinct “winter”, had five males and six virgin females, suggesting that both sexes overwinter on their nest.