A method of preparing a potassium monopersulfate composition is presented, wherein the potassium monopersulfate composition has the formula (KHSO.sub.5).sub.x(KHSO.sub.4).sub.y(K.sub.2SO.sub.4).sub.z, where x+y+z=1 and x=0.46 0.64, y=0.15 0.37, and z=0.15 0.37, said potassium monopersulfate composition having an active oxygen content greater than or equal to 4.9 wt. % and K.sub.2S.sub.2O.sub.8 at a concentration of <0.5 wt. % of the potassium monopersulfate composition. The method includes reacting an H.sub.2O.sub.2 solution containing at least 70 wt. % H.sub.2O.sub.2 with a H.sub.2SO.sub.4 solution at a substoichiometric ratio of the H.sub.2SO.sub.4 to H.sub.2O.sub.2 to generate a weak Caro's acid solution, then combining the weak Caro's acid solution with oleum to produce a rich Caro's acid solution. The rich Caro's acid solution may be combined with an alkali potassium compound to produce the potassium monopersulfate composition. During the process, the temperature is maintained at below 30 .degree. C.