Schiff bases were prepared from S-benzyldithiocarbazate with 5-fluro-, 5-chloro- and 5-bromoisatin. All are potential tridentate nitrogen, oxygen, sulfur donors. They were found to be selectively active against MCF-7 cell line (Human non-metastatic mammary gland adenocarcinoma cell line). The bromide and fluoride compounds were the most active with IC50 values of 6.40 lM (2.6 lg/mL) and 9.26 lM (3.2 lg/mL) respectively while the chloride derivative was weakly active with an IC50 value of 38.69 lM (14.0 lg/mL). The cytotoxic activity of the halo substituted isatins against the breast cancer cell lines tested is in the order of Br[F[Cl. Planarity of the isatin ring in the Schiff bases can be arranged in the following order SB5FISA[SB5ClISA[SB5BrISA while the perpendicularity of the benzyl ring towards the dithiocarbazate plane can be ordered as follows, SB5FISA[SB5BrISA[SB5ClISA.