The Little Belt (Lillebælt, ˈliləˌpelˀt) is a strait between the island of Funen and the Jutland Peninsula in Denmark. It is one of the three Danish Straits that drain and connect the Baltic Sea to the Kattegat strait, which drains west to the North Sea and Atlantic Ocean.
The Little Belt is about long and to wide, and its deepest point is at Marens Hul west of the island of Fænø, at , which makes it deeper than its sister strait, the Great Belt. Numerous small Danish islands lie within the belt. In part because of its depth, 10% of the water moving between the inner Baltic Sea and the Kattegat flows through the Little Belt.
The Little Belt stretches from the town of Juelsminde in the north to the island of Als in the south, with a winding course in between. The northern end is the widest at over . From there it runs southwest, narrowing to about at a place called Snævringen (The Narrows), where the two Little Belt Bridges are located. South of Fænø, the strait widens to about until it reaches the Baltic Sea near Als and the South Funen Archipelago.
The Little Belt's western coastline is largely broken up by irregular inlets called fjords, and both sides feature steep sand bluffs.
The area around the Little Belt is shaped by numerous glacial moraines, the first of which was formed during the early Weichsel glaciation approximately 22-25,000 years ago. Approximately 14-15,000 years ago, during the late Weichsel glaciation, ice arrived from the south and southeast, one part of which became the Little Belt Glacier, causing hilly terrain with deep fjords. The notable tunnel valleys were formed by meltwater. The terminal moraines from the northeast ice's glacial maximum are some of the oldest in Denmark.
The Little Belt is a protected wetland under the Ramsar Convention and a particularly important spot for breeding and migrating birds. Protected species in the area include whooper swans, white-tailed eagles, western marsh harriers, spotted crakes, corn crakes, pied avocets, ruffs, short-eared owls, common terns, Arctic terns, little terns, greater scaups, common eiders, common goldeneyes, and red-breasted mergansers.