Using first-principles calculations, we study the tailoring of the electronic and magnetic properties of gallium sulfide nanoribbons(Ga_2S_2NRs) by mechanical strain. Hydrogen-passivated armchair-and zigzag-edged NRs(ANRs and ZNRs)with different widths are investigated. Significant effects in band gap and magnetic properties are found and analyzed. First,the band gaps and their nature of ANRs can be largely tailored by a strain. The band gaps can be markedly reduced, and show an indirect-direct(I-D) transition under a tensile strain. While under an increasing compressive strain, they undergo a series transitions of I-D-I-D. Five strain zones with distinct band structures and their boundaries are identified. In addition,the carrier effective masses of ANRs are also tunable by the strain, showing jumps at the boundaries. Second, the magnetic moments of(ferromagnetic) ZNRs show jumps under an increasing compressive strain due to spin density redistribution,but are unresponsive to tensile strains. The rich tunable properties by stain suggest potential applications of Ga_2S_2 NRs in nanoelectronics and optoelectronics. Using first-principles calculations, we study the tailoring of the electronic and magnetic properties of gallium sulfide nanoribbons (Ga_2S_2NRs) by mechanical strain. Hydrogen-passivated armchair-and zigzag-edged NRs (ANRs and ZNRs) with different widths are investigated. The band gaps and can be markedly reduced, and show an indirect-direct (ID) transition under a tensile While under an increasing compressive strain, they undergo a series transitions of IDID. They strain a series of transitions of IDID. They also strain tunable by the strain, showing jumps at the Second. the magnetic moments of (ferromagnetic) ZNRs show jumps under an increasing compressive strain due to spin density redistribution, but are unresponsive to tensile The rich tunable properties by stain suggest potential applications of Ga_2S_2 NRs in nanoelectronics and optoelectronics.