In the crystal structures of the title compounds, C15H11Cl2NOS, (1), and C15H11Cl2NO2S, (2), wherein (2) is the oxidized form of (1), the thiazolidine ring is attached to two chlorophenyl rings. The chlorophenyl ring on the 2-carbon atom position points in the same direction as that of the S atom in (1), while in (2), the S atom points in the opposite direction. The O atom on the chiral S atom in (2) is trans to the chlorophenyl ring on the 2-carbon. The chlorophenyl ring planes in each structure are close to orthogonal, making dihedral angles of 78.61 (6) and 87.46 (8)° in (1) and (2), respectively. The thiazolidine ring has a twisted conformation on the S—Cmethine bond in (1), and an envelope conformation with the S atom 0.715 (3) Å out of the plane of other four atoms in (2). In the crystal of (1), molecules are linked by C—H...O hydrogen bonds, as well as by slipped parallel π–π interactions [inter-centroid distance = 3.840 (3) Å] between inversion-related phenyl rings, forming sheets parallel to (001). In the crystal of (2), molecules are linked via C—H...O and C—H...Cl hydrogen bonds, forming slabs parallel to (001).