The relaxation phenomena of two semicrystalline polymers, poly(vinyl fluoride) and poly(vinylidene fluoride) were studied by a dilaitometric technique in the temperature range from—30°C to 200°C. The premelting (Tαc), upper [Tg(U)] and lower glass [Tg(L)] transitions are observed for both polymers, as well as a transition in PVF2which is sensitive to thermal history. Comparison of our results with previous work, in most cases at higher frequencies, as well as thermal treatment of PVF2allow us to make assignments and calculate activation energies for the relaxations. Certain characteristic quantities are given, namely, T < Tg(L)/Tg(L), Tg(L)/Tm, and Tαc/Tm, as well as αΔgand ΔαTg.