In the new supercritical boilers, a combination of tubing is used to achieve mechanical integrity at the most economical cost. The boiler uses dissimilar metal welding (DMW) to obtain the joint. The DMW process poses several challenges that are caused by differences in the physical properties of the base metals. In the present work, the effect of the type of filler metals (Inconel ERNiCr-3 and ERNiCrMo-3) and a buttering process on the creep properties of DMW between ferritic steel T91 and austenitic stainless steel 347H characteristics are presented. Creep testing results show that ERNiCr-3 produced slightly better creep strength compared with ERNiCrMo-3. Nevertheless, the buttering layer has a significant impact on the creep properties. The data was analyzed using the Weld Strength Reduction Factor using time initiation of tertiary creep (WTRF) to material capability. WTRF of direct Welding with ERNiCr-3 and ERNiCrMo-3 both are 0.32 and at 600 °C application. WTRF of ERNiCrMo-3 is 0.6 and on the minimum requirement. WTRF of buttering using ERNiCr-3 is 0.65, and above the minimum requirement of the tube, boiler operated at 600 °C application.