Introduction: Kelakai is a plant often found in South Kalimantan. Kelakai leaves are often consumed as vegetables and are believed to be able to treat various diseases. Kelakai leaves also have antibacterial properties against patho- genic bacteria in the oral cavity. Kelakai leaf extract contains several compounds, such as flavonoids, phenols, tan- nins, and steroids, so that the extract can be an effective mouthwash. Kelakai leaf extract as a mouthwash must be safe for oral tissues whose safety can be known through IC50 value of toxicity test kelakai leaves extract to the BHK- 21 fibroblast cells in vitro. Method: This study was true laboratory experimental with a posttest-only with control group design; consisting of 11 groups with 2 control groups, cell control and media control, and 9 treatment groups of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90%. This study used the MTT assay method in the form of color absorbance value, and the calculation for the percentage of cell viability was conducted. Results: The results of the study show that viability with the concentration of 10-30% was less than 60%, and the concentration of 40-90% was more than 60%, and the IC50 value was 15.196%. Conclusion: Kelakai leaves extract with the concentration of 10-30% has a toxicity effect, while the concentration of 40-90% does not. Based on the IC50 value, kelakai leaves extract does not have a toxicity effect against BHK-21 fibroblast cells.