The antibacterial efficacy of a few filling materials were studied in vitro. Zinc oxide eugenol cement. dycal, cavitec, hipol, cervident, clearfill and microfill were tested against Staphylococcus albus and Lactobacillus acidophilus on thioglycolate agar in order to determine whether the materials are effective inhibitors of bacterial growth. 1. Of these materials tested, zinc oxide eugenol cement was the most effective inhibitor of bacterial growth and revealed about 5.5mm in width of inhibition zone against Staphylococus albus and about 5.0mm against Lactobcillus acidophilus. 2. Dycal was moderate inhibitor of the both bact$={e}$ria showing 2.5mm of the zone in width. 3. Cavitec was the slightest effect against the both bacteria 4. Composite resins tested in this study showed no evidence of inhibiting bacterial growth against the both bacteria.