Mount Hasan (Turkish: Hasan Dağı) is a volcano in Anatolia, Turkey. It has two summits, the 3,069 metres (10,069 ft) high eastern Small Hasandağ and the 3,253 metres (10,673 ft) high Big Hasandağ, and rises about 1 kilometre (0.62 mi) above the surrounding terrain. It consists of various volcanic deposits, including several calderas, and its activity has been related to the presence of several faults in the area and to regional tectonics.

Activity began in the Miocene and continued into the Holocene; a mural found in the archeological site of Çatalhöyük has been controversially interpreted as showing a volcanic eruption or even a primitive map. It was the second mountain from the south in the Byzantine beacon system used to warn the Byzantine capital of Constantinople of incursions during the Arab–Byzantine wars.

The modern name of Mount Hasan is widely accepted to be in dedication to Ebu'l-Gazi (El-Hasan), brother of Ebu'l-Kasım during the reign of the Anatolian Seljuks. It is hypothesized that Mount Hasan's name was "Argeos" or "Argaios", but this name belongs to Mount Erciyes. Another hypothesis is that it was simply called Árgos, (Ancient Greek: Ἄργος) as well as Argeiopolis Mons. The Hittites called it Athar.

Mount Hasan lies in the Anatolian plateau, between the Taurus Range and the Pontic Mountains, and its and Mount Erciyes's silhouettes dominate the landscape and rise high above the surrounding terrain. The city of Aksaray lies 30–40 kilometres (19–25 mi) northwest from Mount Hasan, while the settlements of Helvadere, Uluören, Dikmen and Taşpınar lie clockwise from north to northwest around the volcano. In addition, there are seasonal settlements on the volcano which are associated with summer pastures. The volcano has been prospected as a potential source for geothermal power.

Mount Hasan is part of a larger volcanic province in Central Anatolia known as the Central Anatolian or Cappadocian Volcanic Province., which includes ignimbrites, monogenetic volcanic fields and stratovolcanoes such as Mount Erciyes, Mount Hasan, Karacadağ and Melendiz Dağ with an area of about 20,000 square kilometres (7,700 sq mi)-25,000 square kilometres (9,700 sq mi). Volcanism took place during the Plio-Pleistocene and into the Quaternary.

The volcano has two summits, the 3,069 metres (10,069 ft) high eastern Small Hasandağ/Küçük Hasandağ and the 3,253 metres (10,673 ft) high Big Hasandağ/Büyük Hasandağ, and consist of lava domes and lava flows. Big Hasandağ has two nested craters with an 800 metres (2,600 ft) wide and 200 metres (660 ft) high inner cone that is the source of a lava flow. Whether they are located within a caldera is unclear; rather than one large caldera encompassing the entire complex, there may be a smaller one underlying Mount Hasan specifically. There is periglacial activity on the summit, and fossil rock glaciers are found on the volcano. The volcano as a whole rises almost 1 kilometre (0.62 mi) around the surrounding terrain and covers an area of 760 square kilometres (290 sq mi) with 354 cubic kilometres (85 cu mi) of rocks. The terrain of Mount Hasan is formed by phreatomagmatic breccias, ignimbrites, lahar deposits, lava domes, lava flows and pyroclastic flow deposits. The pyroclastic flow deposits occur in the form of fans or valley flows, when they were channelled by topography. The northern flanks also feature two debris avalanche deposits with hummocky surfaces. Two calderas, the Ulukışla caldera on the eastern and the Keçikalesi on the southwestern flank, adorn the volcano. The volcanics of Mount Hasan have been subdivided into a "hot flow" unit, a "Mt. Hasan ashes" unit and into a lava unit.

Cinder cones, maars and accompanying lava flows also occur around Mount Hasan, they are part of a basaltic volcano family that forms parasitic vents. These include the Yıpraktepe cone/maar and a lava flow field at Karataş which covers an area of 60 square kilometres (23 sq mi) and was produced by fissure vents. Many of the cones around Mount Hasan have been grouped as the Hasandağ-Karacadağ volcanic field.

As a consequence of the subduction and eventual closure of the Neo-Tethys and continental collision between Arabia-Africa and Eurasia, Anatolia moves westward at a rate of 21 millimetres per year (0.83 in/year) between the North Anatolian Fault and the East Anatolian Fault. This movement and the resulting tectonic deformation of Anatolia are responsible for volcanism in Central Anatolia, together with the subduction of the Cyprus Plate. Volcanism has been ongoing for the past 10 million years; it is defined as "post-collisional". Further, volcanism at Mount Hasan has been related to the Tuz Gölü Fault and its intersection with the Karaman-Aksaray faults; the former of these is one of two major fault systems in Central Anatolia which influence volcanism there, and volcanic products of Mount Hasan have been deformed by the fault. The Hasandag fault branches off the Karaman-Aksaray fault and cuts between the two summits of Mount Hasan. It and the Karacaören fault influence the hydrothermal system of the volcano.