Potent cytotoxic copper(II) complexes of furannic semicarbazones were studied in ethanolic solutions at 258C. The four ligands used were synthesized in our laboratory, i.e. 2-furfural semicarbazone (FSC), 5-methyl 2-furfural semicarbazone (MFSC), 2-furfural 4-phenyl semicarbazone (FPSC) and 3-(2-furyl) prop-2-enal semicarbazone (FASC). The mathematical analysis was carried out with a recent computer program SIRKO which indicated the formation of one metal-ligand complex in each case and the logarithm of their stability constants are: log b52.02, 3.84, 4.58 and 4.52 for ligands FSC, MFSC, FASC and FPSC, respectively. A relation between stability and molecular weight of the ligands is proposed which may prove to be interesting as these complexes are being investigated for their cytotoxic activities.