In vitro antitumor activity of various organogallium(III) complexes (1–8) has been tested against CT26CL25, HCT116, SW480 colon cancer cell lines. CV and MTT assays were used to assess on the antiproliferative effect of investigated organogallium(III) complexes. From the investigated complexes, the most active was found to be tetranuclear compound 8 against CT26CL25 cells. Flow cytometric analysis of the CT26CL25 cells upon the treatment with 8 was performed in order to determine the role of apoptosis, caspase activation, autophagy and proliferation rate on the cell death caused with this compound. Results indicate cytotoxic potential of the tetranuclear complex 8 by inducing caspase independent apoptosis and blocking most of the cells before first division.