The Siege of Moji was a siege in 1561 against the castle of Moji in Japan. The castle belonged to the Mōri clan, whose capital was the city of Yamaguchi.

Forces under Ōtomo Sōrin attacked the castle in alliance with the Portuguese, who provided three ships between 500 and 600 tons, each with a crew of about 300 and 17 or 18 cannons. This is thought to be the first bombardment by foreign ships on Japan.

The bombardment permitted the Ōtomo troops to establish themselves around Moji castle. After expending their ammunition though, the Portuguese were forced to withdraw, unable to assist the siege further.

The castle’s defenders nevertheless managed to break the siege lines and reinforce the castle. Ōtomo led an all-out assault on the castle, but the assault failed, and the castle finally remained in Mōri possession.