Helodermoides mongoliensis was named by Sullivan (1979). Its type specimen is AMNH 6669 (left frontal) and is a 3D body fossil. Its type locality is Near Baron Sog, which is in an Eocene terrestrial horizon in the Shara Murum Formation of China. It is the type species of Stenoplacosaurus.

It was recombined as Placosaurus mongoliensis by Sullivan (1979), Estes (1983), Sullivan and Augé (2006); it was recombined as Stenoplacosaurus mongoliensis by Sullivan and Dong (2018).