Midori-ku (緑区) is one of the 18 wards of the city of Yokohama in Kanagawa Prefecture, Japan. As of 2010, the ward had an estimated population of 176,038 and a density of 6,900 persons per km². The total area was 25.42 km².
Midori Ward is located in eastern Kanagawa Prefecture, and on the northwest borders of the city of Yokohama. Except for the northeast portion, much of the area is hilly and relatively sparsely populated compared to other parts of the city. The flatter northeast portion is located on the Tsurumi River basin, with the river serving as a ward boundary with Tsuzuki-ku.
The area around present-day Midori Ward was formerly part of Tsuzuki District in Musashi Province. During the Edo period, it was a rural region classified as tenryō territory controlled directly by the Tokugawa shogunate, but administered through various hatamoto. After the Meiji Restoration, the area became part of the new Kanagawa Prefecture in 1868. In the cadastral reform of April 1, 1889, the area was divided into numerous villages.
During the Meiji period, the area was a center for sericulture. On April 1, 1939, Tsuzuki District was annexed by the neighboring city of Yokohama. In a major administrative reorganization of October 1, 1969, Midori emerged as an independent ward within the city of Yokohama. In 1980, a portion of Midori Ward was transferred to Seya Ward. In 1994, Midori-ku was divided into the present-dau Midori-ku, and Aoba-ku and Tsuzuki-ku.