Protambulyx astygonus is a species of moth of the family Sphingidae first described by Jean Baptiste Boisduval in 1875.

It is known from Bolivia, Paraguay and Brazil.

It is similar to Protambulyx goeldii, but the forewing is lacking the large discal spot and the submarginal line of the hindwing is crenulated and angled outwards on the veins.

Adults are on wing in October in Bolivia.

In Paraguay, adults have been recorded in June.