The effect of austenite (γ) phase stability in the local deformation region on the deformation energy of ferrite (α)-γ duplex stainless steel is investigated using tensile testing. The uniform deformation energy values of both the γ-stable and unstable duplex stainless steels are similar, while the local deformation energy of γ-stable duplex stainless steel is larger than that of γ-unstable duplex stainless steel. In γ-unstable duplex stainless steel, the difference in nano-indentation hardness between the α and transformed martensite (α) phases increases remarkably beneath the fractured surface. Low-voltage electron microscopy observations reveal that voids grow rapidly at the grain boundaries between the α and α phases beneath the fractured surface, resulting in a decrease in the local deformation energy in γ-unstable duplex stainless steel.