Dielectric behavior of semifluorinated n-alkane F(CF2)(n)(CH2)(m)H,(n, m) = (10, 10), (12, 8) has been observed over ranges of frequency and temperature. The distribution parameter of dielectric relaxation time obtained from the Cole-Cole plot is nearly equal to unity. The apparent activation energies for F10H10 and F12H8 are 134.6 kJ/mol and 65.8 kJ/mol, respectively. beta-relaxation was observed which is associated with the rotation of the (CF2)(n) group in semifluorinated n-alkane. The ratio of dipole moment, mu(F12H8)/mu(F10H10) obtained from the Frohlich modification of Onsager’s equation is 2.29, even though these compounds have the same constitution except for two carbons linking to the fluorine or hydrogen atoms. In addition we discuss the time dependence of the dielectric loss factor in the vicinity of phase transition temperatures.