A process for preparing peroxidic perfluoropolyethers having a perioxidic content (PO) lower than or equal to 1.2 of formula A-CF2O(CF2CF2O)m(CF2O)n—(CF2CF2OO)ml(CF2OO)n1CF2—B  (I) Wherein A, B equal to or different from each other are —C1, —F, —F2CC1, —COF, —OCOF, —CF3, m, m1, n, n1 are integers such that the (m+m1)/(n+n1) ratio is between 0.6 and 1.3 and the m/n ration is between 0.5 and 1.2; the number average molecular weight is in the range 35,000-45,000, by tetrafluoroethylene (TFE) photooxidation in the presence of UV light, at a temperature from −80° C. to −40° C., in the presence of a mixture of solvents formed of HFC-227 (hepta-fluoropropane) and a solvent selected between HFC-125 (pentafluoroethane) and FC-218 (perfluoropropane).