Hastelloy C-276 nickel alloy is widely preferred for nuclear power plant applications where steam generators operate at 600 °C. However, stainless steels are still used for tubes in steam gas reformers which necessitates welds between dissimilar materials. In this study, hastelloy C-276 and SS 316 L alloys were joined using GTAW process. The welding parameters of GTAW were optimized to minimize the defects in samples of similar (SS 316 L-SS 316 L, HAS C-276-HAS C-276), and dissimilar (HAS C-276-SS 316 L) joints. SEM/EDS results confirm the presence of columnar dendritic and cellular structure in fusion zone for dissimilar weldments (HAS C-276-SS 316 L). EDS results also revealed the presence of larger amount of Mo, W and lower amount of Ni in the subgrain boundary as compared to the subgrain body. Compared to the similar (HAS C-276- Has C-276) and dissimilar (HAS C-276-SS 316 L) welded joints FZs, the enrichment of Mo is lesser in SS 316 L-SS 316 L similar welded joints. Higher UTS was obtained for dissimilar (HAS C-276-SS 316 L) GTAW joints 780 MPa compared to the similar welded joints of SS316 (552 MPa) and HAS C-276 (740 MPa). The average microhardness for the dissimilar SS 316 L and HAS C-276 is 220 Hv, which is higher compared to the similar welded joints, SS 316 L and HAS C-276, i.e., 190 Hv and 210 Hv, respectively. This study shows that GTAW process is suitable to fabricate sound weld joints of similar (SS 316 L- SS 316 L, HAS C-276-HAS C-276), and dissimilar (HAS C-276-SS 316 L) alloys which are useful for the nuclear power plant boilers. © 2021, The Indian Institute of Metals - IIM.