Nisanzai Kofun is a keyhole-shaped mounded tomb constructed on the southeastern edge of the Mozu area.
The mound length is approximately 300 m, and the height of the square front part is 25.9 m, making it the third largest in the Mozu area.
The mound was surrounded by a double moat when initially constructed.
In the moat on the east side of the round rear part, postholes were detected from the mound slope to the bank. They are apparently traces of a wooden bridge crossing the moat.
During the excavations, cylindrical haniwa (earthenware funerary sculptures) arranged without gaps have been unearthed from the first-tier terrace. A large Sue ware pot was found at the projection, and representational haniwa and sunshade-shaped wooden haniwa have been found in the moat.
The construction period dates to the second half of the 5th century.