Potassium perfluoroalkenyl(fluoro)borates, K[R F BF 3 ], (R F =CF 2 C(CF 3 ), cis-CF 3 CFCF, and cis-C 6 F 13 CFCF) decomposed at 208–225°C (T max , dTG). The K[R F BF 3 ] salts (R F =C 3 F 7 , C 6 F 13 , trans-CF 3 CFCF, and trans-C 4 F 9 CFCF) decomposed at 273–312°C (T max , dTG). Both groups of salts formed volatile polyfluoroorganics and K[BF 4 ] as solid residue. The preparative thermolysis of selected prototypical salts K[R F BF 3 ] showed that the polyfluoroorganics consisted of a mixture of internal perfluorohexenes, C 6 F 12 , and 1-H-tridecafluorohexane, C 6 F 13 H, in case of K[C 6 F 13 BF 3 ], and of perfluorooctynes, C 8 F 14 , and cis-C 6 F 13 CFCFH in case of K[cis-C 6 F 13 CFCFBF 3 ]. The salts K[(C 6 F 5 ) 2 BF 2 ] and K[R F BF 3 ] (R F =CF 3 CC, CF 3 CFCFCC, C 6 F 5 CC, C 6 F 5 , 2,3,5,6-C 5 NF 4 ) decomposed in the temperature range 249–337°C (T max , dTG) and mainly resulted in non-volatile polyfluoroorganics besides K[BF 4 ]. The reaction path of the thermolysis of perfluoroalkyl-, perfluoroalkenyl-, and perfluorophenyl(fluoro)borates is discussed and compared with that of perfluorocarboxylates.