Aim:The aim of this study is to evaluate the minimum inhibitory concentration (MIC) of cinnamon bark oil against Lactobacillus acidophilus and incorporate it in the liquid component of glass ionomer cement (GIC) followed by determination of its effect on the compressive strength. Materials and methods:Antibacterial effect of various concentrations of cinnamon bark oil was evaluated using broth microdilution method with 96-well tissue culture plate. Minimum inhibitory concentration of the cinnamon bark oil against L. acidophilus was determined and that concentration was then incorporated into the liquid component of the GIC, and its compressive strength was evaluated. For compressive strength testing, teflon mold of 4 mm diameter and 6 mm height was used for the preparation of samples. The prepared specimens were stored in distilled water at 37°C for 24 hours in an incubator. After 24 hours, the samples were subjected to the universal testing machine at a speed of 1 mm/minute for compressive strength evaluation. The maximum load required to fracture the specimen was recorded.Results: A volume of 20 µL/mL was found to be the MIC of the cinnamon bark oil against L. acidophilus. The mean compressive strengths of conventional and cinnamon bark oil-incorporated GIC revealed no significant difference. Conclusion:Cinnamon bark oil has antibacterial property against L. acidophilus. Incorporation of 2% v/v cinnamon bark oil did not adversely affect the compressive strength of GIC.Clinical significance: By incorporating this bacteriostatic agent to GIC, the progress of caries and failure of restorations can be prevented by inhibiting the growth of L. acidophilus. Clinically, it can be used in cases of deep dentinal caries, early childhood caries, rampant caries, and patients with high caries index.