1 - week CBBs, a main monetary policy instrument of BoM, plays an important role on managing the reserves of the banks. This CBB rate represents BoM’s policy rate guides interbank money market. In July 2007, the CBB with stable rate and unlimited bidding was introduced with auctions to be held on every Wednesday. This really had attracted the banks’ interests providing the possibility for the banks to place their excess reserve in short term asset. There has been a substantial change in the way banks manage their reserves since then. For the favorable adjustment of CBB rate and loan principle along with the well balance of togrog and foreign exchange, 1 - week CBB has been held in a type of competing by rate since May 2005. The auction average rate is the targeted rate variables in +/-2 percent from the policy rate and it frames to make the interbank rate as the operational target in midterm.