Electrical conductivities and thermoelectric powers have been measured as a function of temperature and composition in AgI-AgBr system. The electronic conductivities in its superionic phase are negligibly small in comparison with ionic conductivities. The composition dependence of activation energies slightly decreases with increasing the bromine concentration. The lattice constant in this phase decreases with increasing the bromine concentration. The reduction of bottle neck size in conducting path of mobile ion, which originated from the decreasing of the lattice constant, produces the enhancement of activation energy. But this prediction is contradicted with the present observations. These behaviors may be attributable to a distortion of crystal lattice. The heat of transport obtained from measurements of thermoelectric power is slightly larger than the activation energy of ionic conduction in the superionic phase. This relation may be qualitatively explained by the model of Fokker-Plank equation.