Laser beam welding was used to join a near-β titanium alloy (Ti-3Al-6Mo-2Fe-2Zr), and afterwards, aging treatment at different temperatures were conducted on the laser welded joints. The relations among aging temperature, microstructure, and tensile properties of joints were revealed in detail. For as-welded joints, the fusion zone features primarily single β phase. The reason is attributed to the high Mo equivalency of this alloy and the fast cooling rate in laser beam welding. After aging treatments, a large amount of α precipitates forms in the fusion zone and HAZ. The rising aging temperature coarsens α precipitates and reduces the volume fraction. Compared with the as-welded joints, the joints’ tensile strength and elongation are improved after undergoing aging treatments. The increasing aging temperature weakens the strengthening effect because of the decreasing volume fraction of α precipitates. After the 500°C/8h aging treatment, 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.