This paper analyzes the influence of credit card transactions on menetary economy. Based on the cash-in-advance model (CIA) established by Stockman (1981), we add the credit line of credit cards into the CIA constraints. We find that credit card transactions have a positive effect on output and will offset the negative effect of anticipated inflation. It implies that the proliferation of credit cards will stimulate consumption, investment and output. The empirical study of Taiwan shows that there are five break points in the proxy time series of credit card transactions during 1993-2001. And we find that the narrower of the definition of money, the weaker the negative effect on output of monetary policy.