The Sukumozuka Kofun is located in the Kushiro Hills at an elevation of about 40 meters near the Masuda River.

It was designated as a National Historic Site on December 13 of the same year as a large circular [ja] enpun (円墳) burial mound; however, the designation was immediately controversial as many archaeologists argued that it was a zenpō-kōen-fun (前方後円墳), which is shaped like a keyhole, having one square end and one circular end, when viewed from above, or else a zenpō-kōhō-fun [ja] (前方後方墳) shaped like two co-joined rectangles.

[2] The issue was only settled in October 2022, when the Masuda City Board of Education announced that findings confirmed the Sukumozuka Kofun to be a keyhole-shaped burial mound.

The surface of the tumulus is covered with fukiishi, the size of a human head, and had two rows of cylindrical haniwa.

There is a 17 x 15 meter square structure on the north side of the circular portion, presumably a ceremonial platform.