Li17-Pb83 eutectic is considered as one of the option for ITER test blanket and breeder blanket of DEMO reactor. Properties of Li-Pb eutectic define the conditions of its application and breeder blanket design and vice versa - operating conditions affect to the properties of eutectic that resulted in structure and properties changes. The paper deals with the structure peculiarities, physical and mechanical properties investigation of Li-Pb eutectic. It was shown that Li-Pb eutectic may deviate from eutectic composition due to structure instability at some working conditions. Long term exposure at high temperature both in liquid and solid state resulted in non-homogeneity of microstructure of Li-Pb alloy. Temperature dependencies of physical and mechanical properties (under compression and tension) and structure stability issues of Li-Pb eutectic and near eutectic alloys were studied. These results are discussed in the paper.