One of the negative consequences of effect of extreme conditions of underwater welding is a low level of properties of welded joints, in the first turn, of ductility. Traditionally, this task is solved by optimization of microstructure of weld metal due to rational alloying. The purpose of this work was to establish the influence of microalloying of weld metal with titanium and boron on its mechanical properties in underwater welding using flux-cored wire. The structure of metal formed as a result of microalloying was investigated, and values of mechanical properties of deposited metal were determined. Optimal proportions of microalloying were established, at which high values of elongation of weld metal are provided. It is shown that its mechanical properties meet the requirements of A class of Specification on underwater welding ANSI/AWS D3.6. 5 Ref., 2 Tables, 7 Figures.