Introduction: Rhodanine is a heterocyclic, organic compound, discovered in 1877. The core of the compund consists of a thiazolidine ring which has a great power of modification. Therefore, it is easy to prepare a laboratory different types of rhodanine derivatives that have shown useful anti-tumor properties during scientific research. It has been proven that rhodanine derivatives are attractive compounds due to their biological activity, antiepileptic, antibacterial and antidiabetic activity. Objective: To investigate the cytotoxic effect of pure rhodanine and its three derivatives (PCI-Ro, C-Ro, P-Ro) on four human tumor cell lines (HeLa, CaCo-2, MCF-7, NCI-H358). Materials and methods: Rhodanine derivatives were synthesized in the Department of Chemistry and Ecology at the Faculty of Food Technology in Osijek (Figure 5), whereas the pure rhodanine was purcahsed as such. For the purpose of the experiment, rhodanine derivatives and pure rhodanine were dissolved in the solution of DMSO and H2O in a 1:1 ratio and prepared as concentrated solutions (10-2mol/dm3). An exception is 3-(4-klorfenil)-2-tioksotiazolidin-4-on, which was prepared by dissolving in pure DMSO. Cultivation of the cells was carried out in an incubator with a 5% carbonic (IV) oxide atmosphere and a temperature of 37 ° C. The vials in which the cells were grown were 25 cm2, and the DMEM medium was used for cell maintenance. Results: It was noticed that survival is above 75% in all compounds, on all cell lines, at concentrations of 10-5 M to 10-7 M. A stronger cytotoxic effect is observed at the highest concentration (10-4 M), but only for PCI-Ro and C-Ro derivatives. PCI-Ro brings to the inhibition of cell growth by 50-65%, while C-Ro inhibits MCF-7 for about 80%, and other cell lines (CaCo-2, HeLa, NCI-H358) for about 55-65%. Conclusion: Rhodanine derivatives reduce the growth of tumor cells. The percentage of inhibition depends on the concentration of the compound and the cell line type.