Hornsund is a fjord on the western side of the southernmost tip of northern Norway's Spitsbergen island.

The fjord's mouth faces west to the Greenland Sea, and is 12 kilometres (7.5 mi) wide.

Hornsund cuts different geological formations, from the Precambrian to the west to the upper Mesozoic to the east, and it is perpendicular to the main regional fractures of Spitsbergen.

The coastline of Hornsund is diversified, with a number of bays at the mouths of mountainous glacial valleys.

The English explorer Jonas Poole visited Hornsund in 1610, giving the fjord its name after his men had brought back a reindeer antler.