Abstract Since the properties of sulfur-containing compounds depend on the sulfur number contained in the compound, it is desirable to develop a method to control the sulfur number. A common method for synthesizing sulfur-containing compounds is to mix sulfur with a base to form linear sulfur, which is then reacted with an organic compound to obtain a sulfur-containing compound. In this study, we systematically investigated the relationship between the type of base, equivalent amount of the base, and the reaction solvent and the sulfur number in the resulting sulfur-containing compound. The sulfur number of sulfur-containing compounds prepared in water was controlled by the equivalent ratio of elemental sulfur (S8) and base. Sulfur-containing compound with high sulfur values was obtained using solvents with low dielectric constants and with lower base equivalents compared to S8.