Bessho Nagaharu (別所 長治, 1558-February 2, 1580) was a Sengoku era daimyo, eldest son of Bessho Yasuharu.
In 1578, Oda Nobunaga called on his retainers to attack the Mōri clan. Nagaharu was ready to take the lead of Oda's troops, but after learning that General Hashiba Hideyoshi, who was of low extraction and whom he did not respect, was allied with the Oda faction, he revolted and instead made an alliance with Hatano Hideharu of Tamba province.
On Nobunaga's order, Nagaharu was then besieged by Hideyoshi's troops. Nagaharu moved to the castle of Miki, which signaled the beginning of the siege of Miki.
The siege does not go well for Hideyoshi, however, and following a rebellion by Araki Murashige and with the help of the Mōri clan, Nagaharu successfully repels Oda's forces.
However, Hideyoshi returns and this time, instead of launching a direct attack, he sets up multiple sieges against small castles such as Kamiyoshi and Sigata in order to cut off Mōri support.
This tactic leads to a rapid depletion of food and, in 1580, with no hope of further reinforcements from the Mōri clan, Nagaharu commits seppuku in exchange for the lives of his soldiers from Miki Castle.