Gansu (UK: , US: ; alternately romanized as Kansu) is a province in Northwest China. Its capital and largest city is Lanzhou, in the southeast part of the province.

The seventh-largest administrative district by area at 453,700 square kilometres (175,200 sq mi), Gansu lies between the Tibetan and Loess plateaus and borders Mongolia (Govi-Altai Province), Inner Mongolia and Ningxia to the north, Xinjiang and Qinghai to the west, Sichuan to the south and Shaanxi to the east. The Yellow River passes through the southern part of the province. Part of Gansu's territory is located in the Gobi Desert. The Qilian mountains are located in the south of the Province.

Gansu has a population of 26 million, ranking 22nd in China. Its population is mostly Han, along with Hui, Dongxiang and Tibetan minorities. The most common language is Mandarin. Gansu is among the poorest administrative divisions in China, ranking 31st, last place, in GDP per capita as of 2019.

The State of Qin originated in what is now southeastern Gansu and went on to form the first known Empire in what is now China. The Northern Silk Road ran through the Hexi Corridor, which passes through Gansu, resulting in it being an important strategic outpost and communications link for the Chinese empire.

The city of Jiayuguan, the second most populated city in Gansu, is known for its section of the Great Wall and the Jiayuguan Pass fortress complex.

1920 Haiyuan earthquake (Chinese: 海原大地震; pinyin: Hǎiyuán dà dìzhèn) occurred on December 16 in Haiyuan County, Ningxia Province, Republic of China at 19:05:53. It was also called the 1920 Gansu earthquake because Ningxia was a part of Gansu Province when the earthquake occurred. It caused destruction in the Lijunbu-Haiyuan-Ganyanchi area and was assigned the maximum intensity on the Mercalli intensity scale (XII Extreme). About 258,707~273,407 died, making it one of the most fatal earthquakes in China, in turn making it one of the top disasters in China by death toll.