The temperature dependences of the molar heat capacity at constant pressure, Cp, of Pb5(Ge1−xSix)3O11 crystals with x=0, 0.39, and 0.45 in the range 5–300 K, as well as of their permittivity, dielectric losses, and the pyroelectric effect, have been measured. Experimental data on the temperature behavior of the heat capacity are presented in the form of a sum of two Debye and one Einstein terms, Cp(T)=0.405CD1(ΘD1=160 K, T)+0.53CD2(ΘD2=750 K, T)+0.046CE(ΘE=47 K, T). Besides a peak in the region of the ferroelectric Curie point Tc=450 K for crystals with x=0, the temperature dependences of the heat capacity did not reveal any other pronounced anomalies.