Guanzi 關子 were a kind of promissory note used during the Song period 宋 (960-1279). There is evidence that similar bills called jindai guanzi 金帶關子 were given to princes or member of the nobility during the Tang period 唐 (618-907) which gradually came into use as a common means of payment.
In the early years of the Southern Song 南宋 (1127-1279), troops were paid by so-called xianqian guanzi 見錢關子, meaning that they were freely convertible into copper coins (xianqian 現錢), yet an exchange fee of 10 cash was due. The bills were circulating around the capital Lin'an 臨安 (today's Hangzhou 杭州, Zhejiang) and particularly designed for the tea merchants from Wuzhou 婺州. Some high officials of the court were arguing against the introduction of the Sichuanese jiaozi 交子 as an official means of payment because they were not sufficiently backed by money (benqian 本錢), so guanzi remained one of the main paper currencies in southeast China after 1131, apart from the huizi 會子.
The court had in 1159 issued guanzi notes with a total value of 800,000 min 緡 (nominally a string of 1,000 cash), to be replaced by fresh ones after a period of three years (jie 界). For the region of Huaidong 淮東, half the amount was produced, with a lifespan of two years, and called gongju 公據. There were five denominations for guanzi bills. Records of the guanzi note a lacking after 1190, which means that huizi had become the most important paper money of the economical centre of the Southern Song empire, apart from the jiaozi note.
Only in 1264 a further attempt was made to reintroduce guanzi, and paper bills with the names tongqian guanzi 銅錢關子, jinyin xianqian guanzi 金銀見錢關子 or yinguan 銀關 (apparently accounted in silver) were produced. It was planned to replace the inflatory huizi notes by this new currency. The exchange rate was 1 guan 貫 (nominally a string of 1,000 cash) of guanzi against 770 copper coins or 3 guan of huizi of the 18th production period. Yet the new currency did not prevent the further decline of paper money in the last years of the Song period.