Abstract In this work, the sensitivity of liquid metal embrittlement of the T91 martensitic steel is investigated with the small punch test (SPT). The material was studied in three tempering conditions (as quenched, tempered at 500 and 750 °C), at 300 °C in air and in the liquid lead bismuth eutectic (LBE). The load–displacement curves (four stages, low maximum force and large displacement to fracture) obtained for one test condition of the 750 °C tempered material is in general very different from those of the two other materials. An effect of LBE has been observed for the as quenched and 500 °C tempered steels. For these materials, the curves tend to be linear with a reduced displacement to fracture suggesting a brittle behavior. This ductile to brittle transition induced by liquid metal has been confirmed from the fracture surface analysis where cleavage was observed. In comparison with conventional tensile tests, small punch tests appear to be more sensitive to evidence liquid metal embrittlement.