Introduction: Due to the constantly growing incidence, colorectal cancer is becoming an increasingly important diagnostic and therapeutic problem. This requires the discovery of new drugs that would affect its reduced incidence and the possibility of cure. Today, attention is increasingly focused on organometallic compounds that stand out for their antiproliferative activity against colorectal cancer. Objective: To test the antitumor activity of the Copper (II) coordination complex with chromone-2-carboxylic acid on cultured spheroids and to determine whether there is a difference in the effect of the compound on tumor Caco-2 and HT-29 spheres compared to normal MRC-5 spheres. Measure the amount of glutathione in the cells as an indicator of the antioxidant effect of the examined Cu (II) complex. Materials and methods: The compound used in the research is a Copper (II) coordination complex with chromone-2-carboxylic acid. The complex was synthesized at the Department of Chemistry, Josip Juraj Strossmayer University Osijek. The antitumor activity of the tested compound was tested by MTT test on 3D cultured spheres. The antioxidant activity of the tested compound was determined by measuring glutathione. Results: The tested complex shows anti-tumor activity on all cell lines, whereby the combination of a single treatment and a higher concentration (1 x 10-5 mol/dm3 ) showed the best effectiveness in stopping the growth of malignant cell lines. The complex showed the most effective antitumor activity on the HT-29 cell line after a single treatment at a concentration of 1 x 10-5 mol/dm3 . The tested complex did not show a significant cytotoxic effect on the normal cell line MRC-5 in any type of treatment, at any concentration. In the MRC-5 cell line, a higher level of reduced glutathione compared to total glutathione was observed. Conclusion: Copper (II) complex reduce the growth of tumor cells.