Laser beam welding was used to join a near-β titanium alloy (Ti-3Al-6Mo-2Fe-2Zr), followed by aging treatments. The relations among aging temperature, microstructure, and tensile properties of joints were revealed. For as-welded joints, the fusion zone features primarily single β phase. It is attributed to the high Mo equivalency of this alloy and the fast cooling rate in laser beam welding. After aging treatments, many α precipitates form in the fusion zone and heat affected zone. The rising aging temperature coarsens α precipitates and reduces the volume fraction of α precipitates. Compared with the as-welded joints, the aging treated joints' tensile strength and elongation are improved. The increasing aging temperature weakens the strengthening effect because of the decreasing volume fraction of α precipitates. After the aging treatment at 500 °C for 8 h, the joints obtain the optimal match between strength and plasticity. The fracture mode of joints changes from quasi-cleavage fracture in as-welded condition to microvoid coalescence fracture after heat treatments.