A mid-infrared (IR) optical parametric amplifier (OPA) in a newly developed wide band-gap nonlinear crystal BaGa4S7 (BGS) was reported for the first time. The BGS-OPA was pumped by a 30 ps pulse 1064 nm laser operating at a repetition rate of 10 Hz. A maximum idler pulse energy of ~130 μJ at 7.25 μm was obtained at pump energy of ~6.9 mJ, corresponding to a pump to idler photon conversion efficiency of ~13%. Moreover, across 6.3–8.8 μm idler tuning range was demonstrated, with output energies of ~66 μJ at 6.3 μm and > 27 μJ over the entire tuning range under a fixed pump energy of ~4.1 mJ. Finally, the corresponding type-I (e → o + o) phase-matching (PM) angles of the generated mid-IR idler light in BGS were measured and compared with the theoretical calculation result based on the reported Sellmeier equations.