This dissertation examines the degree and speed of key retail interest rates in response to prime rate changes in Thailand. By using five deposit rates and three lending rates from 46 domestic and foreign banks between January 1996 and July 2013 at a monthly basis, I am able to investigate the impacts of the oligopolistic structure in the banking sector and the changing financial environment in Thailand on the interest rate pass-through. The results show that the long-run pass-through is higher than the short-run, but neither is complete. All retails interest rates are more rigid when they are below their equilibrium level than they are above. In addition, the oligopolistic structure has a positive impact on the degree of pass-through, but has no impact on the adjustment speed of the pass-through. Finally, changes in the financial environment could affect interest pass-through as introducing inflation targeting policy has increased the pass-through but financial crises have significantly reduced the pass-through. The findings imply monetary policy transmission via interest rate pass-through is less effective but improving overtime in Thailand.