P-glycoprotein (P-gp) is an active drug efflux pump, which exists widely in various MDR tumor cells, conferring drug resistance to tumor cells during chemotherapy. Some 4-thiazolidinone derivatives containing indolin-2-one moiety are novel anti-tumor compounds. The aim of this study was to evaluate the transport activity of P-gp towards 4-thiazolidinone derivatives containing indolin-2-one moiety (as mixtures of 2Z, 5Z and 2E, 5Z isomers) and the transport inhibition activities of the derivatives to P-gp, the results of which could provide crucial information for the further separation of and development on the derivatives with excellent anti-tumor activities. The results indicate that the further separation and development should be focused on compounds 7, 10, 12 and 13 (tumor cell cytotoxic P-gp modulators) and compounds 8, 9, 17 and 18 (non-substrates of P-gp), which exhibit anti-tumor activities and could overcome P-gp mediated MDR. Furthermore, the results of molecular docking indicate that Ser222, a residue in TM4 domain of P-gp, exhibits an intriguing feature in that it interacts with all of the derivatives related with P-gp transport in a significant way, including both typical substrates and modulators of P-gp. Meanwhile, the compounds showing no interaction with Ser222 are mainly from the category of non-substrates of P-gp. Therefore, the interaction between Ser222 and the tested derivative would provide useful information for the further development on 4-thiazolidinone derivatives containing indolin-2-one moiety.