Oppolzer is the remnant of a lunar impact crater that is located on the southern edge of Sinus Medii, along the meridian of the Moon.

It was named after the Austrian astronomer Theodor von Oppolzer.

This formation consists of little more than an irregular arc of mounts along the south, and a ring of scattered ridges along the northern rim.

There is a particularly wide gap in the rim to the northeast where no ridges survive to mark the crater perimeter.

By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Oppolzer.