Mui Tsai (Chinese: 妹仔; Jyutping: mui6zai2), which means "little sister" in Cantonese, describes young Chinese women who worked as domestic servants in China, or in brothels or affluent Chinese households in traditional Chinese society. The young women were typically from poor families, and sold at a young age, under the condition that they be freed through marriage when older. These arrangements were generally looked upon as charitable, as the young women would be provided for better as Mui Tsai than they would if they remained with their family.
The traditional Chinese family needs a male offspring. Poor parents, who were not able to support many children, have sometimes killed newborn infants when they were female. In consideration of the grinding poverty it was an accepted alternative to sell unwanted girls.
The absence of contracts in these arrangements meant though that Mui Tsai might be resold into prostitution. The practice was also prevalent before World War II in Hong Kong, Singapore and parts of Southeast Asia.
In the 16th century it was a common practice in Macau, that poor families sold daughters as domestic servants for 40 years. As the Portuguese settled in Macau they began to establish brothels with Mui Tsais, but the Mandarins intervened.
During the middle of the 19th century the British Slavery Abolition Act and the Slave Trade Act were enacted. The Hong Kong government did not impose any restriction on the transfer of girls as Mui Tsais before 1923, because this was treated as a family matter or traditional custom. Kathleen Simon, Viscountess Simon, fought for several decades to free the remaining Mui Tsai.