The synthesis of 5-substituted 3-methylmercapto-6-methyl-1,2,4-triazines by substitutiorF reactions of N-5'-(3'-methylmercapto-6'-methyl)-1',2',4'-triazinyl]pyridinium chloride (Ⅱ) was reported.On passing hydrogen sulfide into a suspension of compound (Ⅱ) in pyridine at room temperature, or on adding an aqueous solution of sodium hydrogen sulfide previously saturated with hydrogen sulfide to an aqueous solution of compound (Ⅱ), 3-methylmercapto5-mercapto-6-methyl-1,2,4-triazine (Ⅲ) resulted.When hydrogen sulfide was passed into a suspension of compound (Ⅱ) in pyridine at 90-95°, substitution reactions took place both at C₃ and C₅ positions with the formation of 3,5-dimercapto-6-methyl-1,2,4-triazine (IV).Both compounds Ⅲ and IV could be methylated with methyl iodide in aqueous sodium hydroxide solution to the same 3,5-dimethylmercapto-6-methyl-1,2,4-triazine (V).