The magnetic, electrical and magnetotransport properties of spinel-type Mg(Fe0.8Ga0.2)2O4+δ ceramic ferrites have been investigated. The results of the investigations temperature and field dependences of magnetization and resistivity are presented and analyzed. The data of neutron scattering were found to be in good agreement with the Neel model of ferrimagnetism. This compound is magnetomonophase ferrimagnetic in the wide range of temperatures, and shows transition in paramagnet at high temperature (~490 K). Mg(Fe0.8Ga0.2)2O4+δ is characterized by maximal value of magnetization (28 emu/g) in the range of Mg(Fe1−xGax)2O4+δ solid solutions. A negative magnetoresistance (MR) effect has been observed in Mg(Fe0.8Ga0.2)2O4+δ ferrite spinel. It has been determined that coefficient of the negative MR increased from 0.23% (at room temperature) to 7.28% (at 220 K). It can be explained with the help of the spin-dependent scattering on magnetic inhomogeneity of granular boundary.