We have reported the effect of electron donating and withdrawing substituents on absorption and electrochemical properties of formazan derivatives as well as antiproliferative activity. New formazans F2 and F4 bearing electron donating subunits have been synthesized, and characterized via elemental analysis and various spectroscopic techniques. The substituent effects and solvatochromic of formazan derivatives F2-F5 having different substituents on 1-phenyl ring in eleven solvents were investigated by absorption spectroscopy. Whilst their absorption bands are only slightly dependent on the polarities of solvents, the considerable alteration was detected by modifying the electronic characteristic and positions of the substituents. Then, the antiproliferative activity of all compounds was investigated in four cancer cell lines using MTT and XTT assay methods. The IC50 values of F2 and F4, having electron donating methoxy and methyl subunits were obtained in the ranges of 10.60 and 21.53 mu M in DLD-1 and HepG2 cell lines. Our study demonstrates that F2 and F4 are more active than the positive control drug used.