The mechanical behaviour assessment of structural alloys is crucial for the durability and safety of ADS. Moreover, it is well-known that the presence of a liquid metal may compromise the good performances of a metallic alloy due to liquid metal corrosion or liquid metal assisted mechanical damage. Though tough and ductile metallic alloys are selected, they may become brittle when stressed in liquid metal exhibiting thus the so called Liquid Metal Embrittlement (LME). The paper summarizes the results obtained in our lab on the mechanical behaviour of martensitic and austenitic steels in liquid lead and in liquid lead-bismuth (LBE) eutectic. Attention was paid on the influence of two parameters: the oxygen content in the liquid metal and the strain rate. Indeed, the chemistry of the liquid metal, especially oxygen content affects the interface between the steel and the liquid metal by formation of an oxide layer (high oxygen) or decreasing the possibility of protective oxide layer to form (low oxygen). Furthermore, variation in oxygen content or chemistry of the liquid metal (Pb, Pb-Bi) could lead to a modification of adsorption or absorption mechanisms. The mechanical properties in inert environment depend on the strain rate as the effect of liquid metal on the time immersion in the liquid metal. So, the strain rate could be considered as an important parameter concerning the mechanical behaviour of the steel in contact with lead and LBE. The mechanical behaviour of martensitic steel and austenitic steels were investigated in a temperature range from 200°C to 500°C by performing monotonic tests (Small Punch Tests and tensile tests) and low cycle fatigue tests in air and in liquid LBE or/and liquid lead. After tests, cracking and fracture surfaces were analysed by SEM, EDX-SEM, EBSD or ToF-SIMS to characterize and understand the effect of the liquid metal. The effect of the presence of liquid metal will be discussed according to the microstructure of the steels as well as the strain rate and chemistry of liquid metal.