Hot corrosion behavior of Pt + Hf co-modified NiAl coating was evaluated in a salt mixture of Na2SO4/NaCl(75:25, wt./wt.) at 900 degrees C in comparing to Pt modified NiAl coating. Worm-like embossments appeared and developed in Pt+Hf co-modified NiAl coating due to the formation of slack Al2S3 and gaseous chloride bubbles. The fast dissolution of HfO2 during hot corrosion led to the disappearing of diffusion barrier effect of Hf-rich zone and elements like, Ni, Ti and N diffused into the oxide scale. The hot corrosion mechanism of Pt + Hf co-modified NiAl coating and the effects of Hf on this process were discussed in this work.