The purpose of this study is to investigate the impact of deregulation on financial market efficiency in Sri Lanka. The concept of efficiency used here is due to Fama (1970) who defines an efficient market as one in which prices fully reflect all available information. Given the significant expansion of Sri Lanka’s financial markets in the post deregulation period, efficiency is investigated in the context of these markets. To this end, the study employs a number of standard tests for market efficiency including; the expectations hypothesis of the term structure, the Fisher hypothesis, uncovered interest parity, speculative efficiency, real interest rate equalization and tests of capital mobility. Although the overall results presented in this study suggest that Sri Lanka’s financial markets are not fully efficient, the evidence provides significant insight to the performance of these markets. The main policy lesson to be learnt from this analysis is that financial deregulation will not automatically promote market efficiency unless accompanied by positive policy action to reinforce the impact of these reforms. In conclusion therefore, the study makes a number of recommendations which could help to reinforce the impact of financial deregulation on market efficiency.