Nishiyamazuka Kofun, Keyhole-shaped kofun in Tenri, Japan

Nishiyamazuka Kofun is a keyhole-shaped mound in Kayo-cho, Tenri, with its square front pointing north. It measures 114 m long: the round rear mound is 65 m across and 13 m high in three tiers, the front section 70 m wide and 8 m high in two tiers. Fukiishi stones and haniwa have been found on the slopes.

The mound was built in the 6th century and belongs to the Ōyamato Kofun Cluster in the region. This period marks the height of keyhole-mound construction before a shift toward different burial practices occurred.

The mound is identified by some scholars as the true tomb of Princess Tashiraka, wife of Emperor Keitai, though the Imperial Household Agency maintains her tomb at Nishidonozuka Kofun. The theory rests on the mound's date in the early 6th century and on haniwa supplied from the same kiln as the emperor's tomb. The name Nishiyamazuka refers to its location on the western edge of the Kayo settlement.

The site can be reached through the Yamanobe-no-michi path, which connects multiple historical locations in the area. Walking this trail gives you a chance to explore other kofun sites and ancient places nearby.

The burial chamber is unknown, but when the summit was ploughed in 1887, a stone coffin came to light along with magatama and kudatama beads, bells, pottery and artificial stone, all now lost. The mound is also the only large late-period keyhole tomb among the mostly earlier Ōyamato cluster.