The facility INTEREST RATE is one of the most important macroeconomic variables. The bank facility INTEREST RATE is associated with other macro-economic variables, one of which is the bank deposit INTEREST RATE. Using the time series data of the 1973-2017 period and the simultaneous equation system, the researchers esti-mated four equations using the three-stage least squares method. The result of estimation of the equation's indicate that there are (i) a significant positive rela-tionship between the bank deposit INTEREST RATE and the facility INTEREST RATE in the Iranian economy during this 45-year period, (ii) a significant positive relationship between the facility INTEREST RATE and the deposit INTEREST RATE, (iii) a significant positive relationship between the liquidity level and the inflation RATE, and there is a positive and relatively significant relationship between the exchange RATE and the inflation RATE, (iv) a significant positive relationship between the facility INTEREST RATE and the credit risk.