Theretra japonica is a moth of the family Sphingidae first described by Jean Baptiste Boisduval in 1869.

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.