The small punch test (SPT) is a relatively new mechanical testing technique capable of utilising small disk-shaped specimens to determine the mechanical behaviour of the test materials. From the test data, fracture properties in particular the equivalent fracture strain (εqf) can be determined and the elastic-plastic fracture toughness of a material can be characterised. Finite element analyses (FEA) of the small punch tests have been performed for the 304H stainless steel in this study. 304H stainless steel was isothermally aged at 650, 700 and 750oC for durations up to 200 hours. Small punch tests were performed to assess the mechanical properties of the heat treated materials. Using the input of the true stress-strain curves of material constitutive behaviour, the theoretical load vs punch displacement curves calculated from the FEA models were found in good agreement with the experimental results. The fracture thickness of the small punch tested specimens and the equivalent fracture strain were also be determined for the test materials.