There is provided is a process for producing a sulfur-containing α-hydroxycarboxylic acid compound represented by the formula (2): wherein R1 represents hydrogen, C1-8 alkyl, or C6-20 aryl, which comprises subjecting a sulfur-containing ketol represented by the formula (1): wherein R1 is the same as defined above, to the action of microbial cells of a microorganism belonging to the genus Pseudomonas, Rhodococcus or Bacillus capable of converting the ketol into a corresponding α-hydroxycarboxylic acid compound, or a treated material thereof, thereby producing the sulfur-containing α-hydroxycarboxylic acid without using a hydroxynitrile compound as a starting material.