Nishiumazuka Kofun is a square mounded tomb constructed 180 m southeast of the round rear part of Hakayama Kofun . Since it was built in Hakayama Kofun’s surrounding area, there is a theory that this tomb is related to Hakayama Kofun.
The mound length is 45 m, and its height is 9.4 m. The mound is surrounded by a moat, but it is preserved underground. Cylindrical haniwa, representational haniwa, and Sue ware (stoneware) have been excavated from the site.
The construction period dates to the second half of the 5th century.