An investigation has been made of the group and individual composition of the products of thiomethylation of butanone by formaldehyde and a mixture of sodium sulphide, hydrosulphide and mercaptides of sulphide-alkaline solutions. It has been established that the reaction products are a mixture of keto-and diketosulphides of aliphatic and cyclic structure, the ratio of which depends on the qualitative and quantitative composition of the sulphur compounds present in the sulphide-alkaline solutions. The amount of cyclic structures increases with increasing temperature (up to 50-80 degrees C) and increasing reaction time. In concentrates of ketosulphides, 3,7-dimethyl-5-thianonane-2,8-dione (I), 3-methyl-5-thiahexan-2-one (II), 3-methyl-5-thiaheptan-2-one (III), 3,6-dimethyl-5-thiaheptan-2-one (IV), 3-methylthiacyclohexan-4-one (V) and 1,4,5-trimethyl-7-thiabicyclo[2,2,2]octan-2-one (VI) and cis-and trans-3,4,6-trimethyl-2-cyclohexen-1-ones (VII) have been identified, the content of compound I reaching 24.5-38.8 wt.%.