The antimicrobial action of various dental cements evaluated against common micro-organisms most frequenty found within the components of the normal bacterial flora of oral cavity. They include Streptococcus mutans (2 strains), Lactobacillus acidophilus, Actinomyces viscosus, and Streptococcus sanguis. The test was done by the use of brain heart infusion (BHI) agar plates. A standard mix of each cement was made and placed on the plates which were seeded with a standard culture of microorganisms. After incubation, the halo of bacterial growth inhibition around the cement was identified and its size was measured. Some of the cements tested had obvious antibacterial effect. The cements listed in decreasing order of effectiveness are 1) zinc phosphate and oxyphosphate, 2) silicate, 3) zinc oxide-eugenol, 4) calcium hydroxide, and 5) carboxylate.