The rate constants for the reaction of n-pentyl iodide and sulphite ion have been determined in varying composition of aqueous methanol. Effects of temperature and alkali metal sulphates on this reaction have also been examined. The influence of varying concentrations of sodium lauryl sulphate (NaLS) and cetyltrimethyl-ammonium bromide (CTAB) at different temperatures on the rate have been studied. Combined effect of NaLS and salts, NaLS and solvent compositions containing less water have caused retardation of the rate. The overall reaction has been found to be second order. The thermodynamic quantities have been calculated in presence and absence of NaLS for the reaction and discussed.