The aim of the present work is to investigate the role of Ni-based filler on Charpy impact toughness (CIT) of the P91 welds joint. The Gas Tungsten Arc Weld (GTAW) joint of creep strength enhanced ferritic/martensitic P91 steel was produced by using the dissimilar Ni-based IN617 and IN718 filler. The welds joint subjected to varying post-weld heat treatment (PWHT) in the temperature range of 650?810 ?C. Post weld normalizing based tempering (PW 4) was also carried out at a normalizing temperature of 1040 ?C.The weld metal shows the cellular dendrites and equiaxed dendrites for IN617 filler along with the segregation of the secondary phase particles at inter-dendritic areas and boundaries. For IN718 filler, columnar and cellular dendrites with well-defined primary and secondary arm were observed along with segregation of the particles at inter-dendritic areas and boundaries. PW 4 provides the uniform distribution of the particles inside the austenitic matrix of weld metal for both filler condition. The CIT test was conducted at room temperature for each condition of the filler and PWHT.The CIT value of the WFZ was measured maximum for as-welded condition and showed a minute change after the PWHT. However, a significant decrease in CIT was measured after the PW 4 for both the filler. ? 2021 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Materials, Processing \& Characterization.