Kayi, Soninké: Xaayi) is a city in western Mali on the Sénégal River with a population of 127,368 at the 2009 census.

The important trading center of Goundiourou, known in Arabic sources as Ghiyaru, was just across the river, and was later rebuilt just south of the modern city.

Guéssé Sidy, a prince of Khasso, established a base there to protect the western approaches to the kingdom's capital, Medina.

In 1881 the French chose it as the site for a fort and barracks, the headquarters of the colonial presence in the central Sudan, as Medina was difficult to access by boat.

[6] From the beginning, the French began building a railway linking Kayes, the furthest point reachable by boat on the Senegal river, with Bafoulabe upstream.

[10] Kayes is nicknamed the "pressure cooker of Africa" due to its extreme heat; the town is surrounded by iron-rich mountains which contribute to the temperature.