A study is performed of the magnetic and dielectric properties of Sr2MnTiO5.87 double perovskite. The origin of the magnetic phase transitions observed in the FC and ZFC magnetization and magnetic specific heat curves at 12 and 43 K is discussed. The Debye and Einstein temperatures, determined by analyzing the lattice contribution to the specific heat, are found to be θD = 217 K, θЕ1 = 275 K, θЕ2 = 615 K, and θЕ3 = 2000 K.