Process for preparing a powdery organic peroxide formulation, said process comprises the following steps: a) preparing a reaction mixture comprising: 40-80 wt % water 10-25 wt % of an acid chloride or chloroformate, 1-4 wt % hydrogen peroxide, 2-8 wt % alkali metal hydroxide, 1-25 wt % of a phlegmatizer selected from the group consisting of ethylene glycol dibenzoate, phenyl benzoate, trimethylol propane tribenzoate, glyceryl tribenzoate, ethylene glycol ditoluate, 1,3-propanediol ditoluate, ethylene glycol 4-tert-butylbenzoate, ethylene glycol monobenzoate monotoluate, 2,3-butanediol dibenzoate, 4-methylphenyl benzoate acid ester, trimethylolpropane dibenzoate, and combinations thereof 0.002-0.20 wt % of a surfactant, and 0.25-5.0 wt % of an inert organic solvent, all percentages based on the weight of the reaction mixture, b) heating the reaction mixture at a temperature in the range 5-50° C.