Abstract: CO2 laser welding of Ti-15V-3Cr-3Al-3Sn to Ti-4.5Al-3V-2Fe-2Mo was conducted in the study. The notched fracture and microstructures of the weld metal (WM) with various post-weld aging treatments were studied. In the as-welded sample, the WM comprised only β phase, which was relatively soft and ductile. Moreover, the phase constituent of the as-welded WM was related to the Al and Mo equivalents and further compared with other welds. The microstructural morphologies and microhardness of the WMs of dissimilar welds exhibited significant changes after post-weld aging at distinct temperatures. Increasing the Al equivalent ([Al]EQ) of the WM caused an increased response to age-hardening during post-weld aging treatments. When the aging temperature was increased from 426 to 593 °C, the α precipitates in the WM grew in size, causing a decrease in hardness, but an improvement in toughness.