Magnetic and dielectric properties of Sr2MnTiO5.87 double perovskite have been studied. Magnetic phase transitions were observed at 12 and 43 K in the FC and ZFC curves of magnetization and magnetic heat capacity, the nature of which is being discussed. From the analysis of the lattice contribution to the specific heat, the Debye and Einstein temperatures were determined, which were θD = 217 К, θЕ1 = 275 К, θЕ2 = 615 К, θЕ3 = 2000 К.