To efficiently separate a sulfur component from an organic solution containing the sulfur component and especially in a production of lactam by subjecting a cycloalkanone oxime to a Beckmann rearrangement using a sulfur compound such as thionyl chloride to efficiently separate the sulfur component from the reaction mixture.

The method for separating a sulfur component in an organic solution includes treating the organic solution containing the sulfur component with an aqueous alkali solution, namely, washing the organic solution containing the sulfur component with an aqueous alkali solution.