The kinetics of alkaline phosphatase catalysed hydrolysis of p-nitrophenyl phosphate in aqueous carbonate-bicarbonate buffered medium as well as in (buffered water-AOT-decane) microemulsion has been studied. Enhancement of reaction turnover has been found in the latter which depends on the mole ratio (w) of [H2O]/[AOT] with a maximum at w = 18.6. The kinetics has a maximum at pH 10.2, the effect being sharper in the microemulsion medium. The activation parameters for the process as well as the energetics of the Michaelis complex at pH 10.2 and w = 18.6 have been evaluated. The surfactants sodium cholate, AOT and cetyltrimethylammonium bromide exhibited complex non-competitive inhibition both in aqueous and microemulsion media.