The main aim of the study was to evaluate the impact toughness behaviour of the precipitation hardened stainless steel (PH 15-7 Mo (Cu), 6.4 mm thick) welded autogenously (without filler) using electron beam welding (EBW). Welds were subjected to various post weld heat treatments (PWHT), like Solutionising (1050°C, 0.5 h, air cooled, a.c). Destabilising (760°C, 2.5 h, a.c) and Aging (450°C/3 h, a.c, 480°C/4 h, a.c and 550°C/1 h, a.c). Charpy V-notch impact toughness of weld metal, heat affected zone (HAZ) portions were evaluated and compared with their base metal counterparts. The study has shown that electron beam welding did not decrease the weld metal and heat affected zone toughness values compared to the base metal toughness in the solutionised + destabilised + peak aged (450°C/3 h) condition (which was 35 J). No post weld heat treatment decreased the toughness of weld metal and heat affected zone compared to the base line toughness (35 J) except for destabilisation followed by aging (450°C/3 h). It was found to lower the base metal toughness values, though not significantly. The ideal post weld heat treatment, which was found to cause smoother hardness profiles, maximum hardness and moderate toughness was solutionising (1050°C) followed by destabilisation (760°C) and peak aging (450°C/3 h).