A comparative study of the thermodynamic and magnetic properties of the Ga-substituted magnesium ferrite polycrystalline samples Mg(Fe_1-x Ga _x )₂O₄ with x = 0.2 and x = 0.4 was carried out. The low-temperature heat capacity of the sample with x = 0.2 was measured by adiabatic calorimetry. Based on the smoothed heat capacity data C _p,m°(T) for Mg(Fe_0.8Ga_0.2)₂O₄, the standard thermodynamic functions were determined in a temperature range 2-800K. A broad heat capacity anomaly below 60K, which can be attributable to the magnetic order-disorder transition, was observed for both samples. The field-dependence of magnetizations in an applied magnetic field up to ± 50kOe revealed the ferrimagnetic behaviour of the samples. The values of Curie temperature (T _C ) and the blocking temperature (T _B ) were determined from ZFC-FC magnetization measurements. Based on the results of heat capacity and magnetic measurements, the low temperature state in the Mg(Fe_0.6Ga_0.4)₂O₄ sample may be attributed to a spin glass-like state.