The aim of the research: The aim of this research is to examine the potential cytotoxic effects of plant species extracts of Raphanus sativus (L.) and Brassica rapa (L.) on human carcinoma cells of breast MDA-MB-231 and bladder T24. It is assumed that the number of cancer cells will decrease after exposure to the extracts in comparison to the control group. Materials and methods: The cytotoxicity on breast and bladder cancer cell lines was tested by the MTT method. It is used to determine the percentage of metabolically active cells after exposure to microwave extracts of plant species Raphanus sativus (L.) and Brassica rapa (L.). Plant samples were prepared in different concentrations and the effect is seen after 4, 24, 48 and 72 hours. The efficiency of the extracts was observed spectrophotometrically by measuring the absorbance at 570 nm. By comparing the absorbance of the formed formazan in cells treated with plant samples and the absorbance of the control (non-treated cells), we obtained the survival rate of cancer cells. Results: The results are graphically presented in relation to the incubation time and the percentage of metabolically active cells. In breast cancer cells, most samples had the greatest cytotoxic effect at concentrations of 50 μg/mL, 75 μg/mL and 100 μg/mL after 72 h of incubation. The most significant effect was achieved with the black radish sample, obtained by microwave extraction, at a concentration of 100 µg/mL, where after 72 h the number of metabolically active cells decreased to 48%. In bladder cancer cells, most samples had the greatest cytotoxic effect at higher concentrations after 48 and 72 h of incubation. The most significant effect was achieved with the white turnip sample, obtained by microwave extraction, at a concentration of 50 µg/mL, where after 72 h the number of metabolically active cells decreased to 16%. Conclusions: In vitro exposure of breast cancer cells MDA-MB-231 and bladder cancer T24 to samples of black radish and white turnip, obtained by microwave extraction, leads to decrease in the survival of these cells. The tested extracts show a cytotoxic effect depended on the incubation time and concentration. Effect of extracts is not always proportional to the increase in incubation time and concentration and in some cases cell recovery occurs. The greatest cytotoxic effect on the MDA-MB-231 cell line was achieved by black radish microwave extract after 72 h of incubation and on T24 cell line by white turnip extract after 72 h of incubation. The cytotoxic effect of the extracts of Raphanus sativus (L.) and Brassica rapa (L.), which was also the hypothesis of our research, was confirmed. The next step is the confirmation of these effects by in vivo studies on the models of animal breast and bladder cancers.