Vicinal perfluorodi-t-butoxycycloalkanes and isomers have been prepared in 50 to 70% yields through photochemical reactions of (CF3)3COOC(CF3)3 with perfluorocycloolefins (c-C5F8 and c-C6F10) under a 200-watt Hg lamp at −20°C. The two isomers of vic-C5F8[OC(CF3)3]2 in 1:4 ratio have been fractionated and identified as cis- and trans-isomers respectively. The three isomers for vic-C6F10[OC(CF3)3]2 in 1:4:2 ratio have been fractionated and tentatively identified as equatorial-equatorial, axialequatorial and axial-axial respectively. New 2,2′ -perfluorodimethoxycycloalkyls have been prepared in 60 to 80% yields through photolysis of CF3OOCF3 with perfluorocycloolefins under a 2500-watt Hg-Xe lamp at −20°C. The attempted separations of the rotational isomers have been unsuccessful. The need of a strong ultra-violet source for primary perfluorodialkyl peroxide is discussed and the mechanism and the radical chain sequences are presented. Another new synthesis of bis(perfluoro-t-butyl) peroxide [D(CF3)3CO-OC(CF3)3 ⋍34.5 kcal] from (CF3)3COF using difluoroamino radicals as the fluoroxy fluorine atoms acceptor is described.