Two-dimensional Janus monolayers have outstanding electronic and transport properties due to their asymmetric atomic structures. In the present work, we systematically study the structural, electronic, and transport properties of the Janus GaInX2(X= S, Se, Te) monolayers by using the first-principles calculations. The stability of the investigated monolayers is confirmed via the analysis of vibrational spectrum and molecular dynamics simulations. Our calculations demonstrate that while GaInS2and GaInSe2monolayers are direct semiconductors, GaInTe2monolayer exhibits the characteristics of an indirect semiconductor. The band gap of GaInX2decreases when the chalcogen elementXvaries from S to Te. Obtained results reveal that small spin-orbit splitting energy in the valence band is found around the Γ point of the Brillouin zone when the spin-orbit coupling is included. Interestingly, GaInS2and GaInSe2have high and directional isotropic electron mobility meanwhile the directional anisotropy of the electron mobility is found in the Janus GaInTe2monolayer. Our findings not only present superior physical properties of GaInX2monolayers but also show promising potential applications of these materials in nanoelectronic devices.