The direct reaction calorimetric method was used for the determination of the formation enthalpy of alloys which concentrations correspond to the: Ga7Li2, Ga9Li5, GaLi, Ga4Li5, Ga2Li3, and GaLi2 intermetallic phases. The obtained experimental values of the formation enthalpy were: −18.1 ±0.8 kJ/mol at., −26.5 ±0.3 kJ/mol at., −34.7 ±0.3 kJ/mol at., −33.5 ±0.5 kJ/mol at., −32.8 ±0.3 kJ/mol at. and −24.6 ±1.4 kJ/mol at., respectively. After the calorimetric measurements, all the samples were checked by way of X-ray diffraction investigations to confirm the structure of the measured alloys. All the measured values of the formation enthalpy of the Ga-Li alloys were compared with literature data and the data calculated with use of the Miedema model.