Weldability of rail steel plays a huge role in joining of rails (joint welded by means of thermite welding or contact electric welding) manufactured in different factories that is one of the most common rail seam welding worldwide. Latvian Railway has been used rail profile 60 E1 manufactured by an English company "Arcelor Mittal" for the last 5 years both on the main railway tracks and elements of crossing pieces (counter-rails, tongue pieces, stock rails, switch blades). In order to ensure safety, reliability and durability of welded rail joints a decision was made to conduct a research of weldability of rail steel type R350HT. An analysis of highly defective rails in the welded seams in Latvian railway during years of 2014, 2015, 2016, 2017 and 2018 was performed within the framework of the research. A detailed research of chemical composition of rail steel of R350HT manufactured by the English company Arcelor Mittal (in the head, web, base) was performed with optical emission spectrometer PMI Master PRO. The obtained data were compared to the Quality Certificate 3.1 EN 10204/EN10168 issued by the manufacturer's factory. The main weldability parameters were calculated with mathematical calculations and formulas: 1. Likelihood of hot cracks during the welding or build-up welding according to Wilkinson index (HCS) 2. Weldability equivalent We, % 3. Heat-up temperature, t, oC 4. Total carbon equivalent, Ctotal, % Structure of the rail steel R350HT was determined and main conclusions were made regarding the weldability of rail steel according to main equivalent index We, % in the final stage of the research.