Theretra sugii is a moth of the family Sphingidae. It is known from the Philippines. The length of the forewings is 40–43 mm. It differs from all other Theretra species in the forewing shape, which is acute apically, concave below the apex on the outer margin and rounded at the tornus, giving a very broad-winged appearance. The antennae are very long, reaching beyond the discal spot. The forewing upperside is similar to Theretra queenslandi. The costal area, discal cell and area beyond the fourth postmedian line are dark olive green, contrasting with the reddish-grey ground colour. The forewing underside is dark reddish brown and lacking continuous transverse lines. It is however, intensely speckled with small dark dots.