The most important commercial activity of the monasteries was "Chang Sheng Ku". The "Chang Sheng Ku" was pawnbroker. Pawnshop was began by the Buddhist monasteries in the early fifth century and only later become common in secular society. It was a high interest loans in the T'ang. The interest rates frequently fifty percent. "Chang Sheng Ku" was one of the commercial organizations that operate by Buddhist monasteries in the Sung dynasty. People who manage monasteries use donations from cash and rent of properties of followers to run business such that loan. A contract that contracted to make sure how much the interest is, what the interest rate per month is and ways to use. This contract let people who manage monasteries can not arbitrarily change the use of interests. Because "Chang Sheng Ku" makes high profit, every monastery always sets one or several "Chang Sheng Ku". Generally, the regular expense of a monastery is buying certificates of monks (Because government have to sell these certificates to compensate financial difficulty.) That is why "Chang Sheng Ku" also be called "Du Shen Jiu". Some monasteries buy farms or cultivated land to get fee of meal by "Chang Sheng Ku". Some monasteries use "Chang Sheng Ku" to buy kerosene of lights in those monasteries, so the "Chang Sheng Ku" was called "Wu Jin Deng" in those monasteries. In the Sung and Yuan period, "Chang Sheng Ku" almost exists in every monasteries. A special monk, who takes responsibility of "Chang Sheng Ku", should make an account balance every month, and do it again in the end of the year. The balance book should be read in public to check mistakes.