The purpose of the study was to synthesize and evaluate the antimicrobial effects of two monophosphazenes, N-diphenylphosphoryl-P-triphenylmonophosphazene-II and N-di(o-tolyl)phosphoryl-P-tri(o-tolyl)monophosphazene-III on bacterial and yeast strains. The biological effects of these molecules were compared with a potential antioxidant vitamin E. According to results, the triphenyl monophosphazene-II has antimicrobial effect on all the bacterial and yeast cells, but tri(o-tolyl)monophosphazene-III has only antimicrobial effect on some bacterial cells. When the concentration of triphenyl monophosphazene-II was raised, it was observed that inhibition zone increased on the bacterial growth media. The biological effects of these molecules were compared to vitamin E in the Saccharomyces cerevisiae culture media. In 200 microg administered culture media, the cell density decreased in vitamin E, triphenyl monophosphazene-II and tri(o-tolyl)monophosphazene-III groups at the end of 24 and 48 h incubation times (p<0.001,p<0.05). While the cell densities in vitamin E and tri(o-tolyl)monophosphazene-II groups decreased partly at the end of 72 h incubation time (p<0.05), its level in triphenyl monophosphazene-II group increased (p<0.01) at the same incubation time. In 1,000 microg administered culture media, cell density was not found to differ between vitamin E and control groups at the end of 24h incubation time, but it was found that the cell densities in triphenyl monophosphazene and tri(o-tolyl)monophosphazene-III groups decreased at the same incubation time (p<0.001). The cell densities in tri(o-tolyl)monophosphazene-III group and triphenyl monophosphazene-II decreased at the end of 48 h incubation time (respectively, p<0.05,p<0.001). In 200 microg administered cell pellets, while the lipid level was not found to differ between control and vitamin E, the lipid level decreased in triphenyl monophosphazene-II and tri(o-tolyl)monophospazene-III groups (respectively, p<0.001,p<0.01). In 1,000 microg administered cell pellets, it was found that the lipid level decreased in vitamin E, triphenyl monophosphazene-II and tri(o-tolyl)monophosphazene-III groups (p<0.001,p<0.01).