Why some people swear to never get married? Many have taken a vow of celibacy beyond apparent religious concerns.To address this question, we study a group of women called Sworn Spinsters (Zishunü) in Southern China.They emerged around the end of the 19th century and almost all of them worked in silk reeling factories.With the fall of Chinas silk industry and the outbreak of wars around the beginning of 1930s, most migrated to Hong Kong and Singapore to work as domestic servants.We present data showing that their openly taking a vow of celibacy made their employers pay more to them relative to their counterparts who did not take a vow.We use a model to explain how the vow increases their value when they work as silk factory workers and domestic servants: openly taking a vow of celibacy heavily taxes a girls marriage opportunity, making her much less likely to quit her job for marriage.The vow is thus the girls credible commitment device of high-intensity labor supply,inducing her employer to invest more human capital on her, or matching her to more important working positions.We present historical details to argue why collectively taking a open vow was likely to be the least costly commitment device, relative to a bilateral labor contract between a girl and her employer.Various bizarre local phenomena, such as nominal marriage, strong sisterhood, twisted customs, extreme religions,and widespread homosexuality can be understood as enforcement mechanisms of the celibacy vow.We also shed light on why for girls taking a vow of celibacy for their careers in modem days would unlikely be the least costly commitment device relative to other types of contracting.