Theretra japonica is a moth of the family Sphingidae. It is found in Japan, China, Korea and Russia. The wingspan is 55–80 mm. The moth flies from May to September depending on the location. The caterpillars feed on a wide range of plants. Recorded food plants are:In China: Cissus, Colocasia, Hydrangea, Parthenocissus, Ampelopsis, Ipomoea batatas, Cayratia japonica, Vitis and Ludwigia. Recorded in Korea on Colocasia antiquorum, Oenothera erythrosepala, Circaea mollis and Hydrangea paniculata. In Japan they feed on Hydrangea paniculata, Ampelopsis glandulosa, Cayratia japonica, Circaea, Fuchsia, Oenothera biennis, Oenothera stricta, Parthenocissus tricuspidata and Vitis. In the Russian Far East they are found on Vitis amurensis.