Xiaolongbao (Chinese: 小籠包; lit. 'little basket bun'; IPA: /ˈʃaʊlɒŋˌbaʊ/) is a type of Chinese tangbao (汤包), traditionally prepared in a xiaolong, a small bamboo steaming basket. The xiaolongbao originates from the city of Changzhou in Jiangsu province, and is an iconic dish of Jiangnan cuisine.

Different cities across the Jiangnan region have varying styles of xiaolongbao. Outside of China, the Nanxiang xiaolongbao associated with Shanghai is the most well known. In the local Shanghai dialect, they are known as siaulon moedeu or xiaolong mantou, as Wu Chinese-speaking peoples use the traditional definition of mantou, which refers to both filled and unfilled buns. The Suzhou and Wuxi styles are larger (sometimes twice as large as a Nanxiang xiaolongbao) and have sweeter fillings. The Nanjing style is smaller with an almost translucent skin and less meat.

In English, the xiaolongbao are often referred to as "soup dumplings", but "soup dumpling" in Chinese may translate to the broader culinary category known as tangbao, which includes the xiaolongbao and other related dishes.

Xiaolongbao originated in Changzhou, Jiangsu province, created by Wan Hua Tea House during the reign of the Daoguang Emperor (1820–1850). It evolved from the guantangbao (soup-filled dumplings/buns) of Kaifeng, Henan province, which was the capital city of the Northern Song Dynasty (960–1127).

There are numerous styles of xiaolongbao in Jiangnan cuisine. Shanghai-style xiaolongbao originated in Nanxiang, which was a neighboring village of Shanghai in Jiangsu that eventually became an outer suburb of Shanghai's Jiading District. The inventor of xiaolongbao sold them in his first store in Nanxiang next to the Guyi Garden. From there xiaolongbao became popular in downtown Shanghai and promptly spread outward.

Chinese buns, in general, may be divided into two types, depending on the degree of leavening of the flour skin. Buns can be made with leavened or unleavened dough. Those made with unleavened dough use clear water for mixing; the skin is thin and the fillings large. It is frequently made in Nanxiang but is imitated elsewhere, called “Xiang-style”. Steamed buns made with raised flour are seen throughout China and are what is usually referred to as mantou. Steamed xiaolongbao made with partially raised flour are more commonly seen in the south. This means that their skin is tender, smoother, and somewhat translucent, rather than being white and fluffy. As is traditional for buns of various sizes in the Jiangnan region, xiaolongbao is pinched at the top prior to steaming, so the skin has a circular cascade of ripples around the crown.

Xiaolongbao are traditionally filled with pork. More modern innovations include other meats, seafood, shrimp, crab meat, and vegetarian fillings. For example, the renowned restaurant Din Tai Fung, famous for its xiao long bao, has launched yam, red bean and chocolate xiao long bao in their vegetarian menu.

Soup dumplings are created by wrapping solid meat aspic inside the skin alongside the meat filling. Heat from steaming then melts the gelatin-gelled aspic into soup. In modern times, refrigeration has made the process of making tangbao during hot weather easier, since making gelled aspic is much more difficult at room temperature.