Macrodactylus argentinus is a species of beetle of the family Scarabaeidae. It is found in Argentina.

 Adults reach a length of about 8.5–9 mm. They are blackish-blue, often transitioning into more or less brown. The head is punctate and the antennae are reddish-yellow, with a blackish-brown club. The pronotum is sparsely punctate in the middle, more densely punctate at the sides, and the punctures are covered with grey or yellowish-grey hairs. The elytra of the males are widely covered with whitish setae, while those of the females are fairly densely covered with yellowish scale-like setae. The sides of the elytra, however, are sometimes glabrous. On the underside, the pubescence is denser than on the upper side.