Tooth decay or erosive wear often results from the contact of acid with hydroxyapatite in tooth enamel. Traditional methods for restoring enamel involve fluoride-based products, but frequent fluoride intake can lead to fluorosis, deterring consumers. This study aimed to investigate the potential of chitosan hydrochloride (mushroom-sourced, vegan-friendly) and chitosan (chitin-sourced) in enhancing the acid resistance of bovine enamel blocks in vitro. Enamel blocks were sectioned from bovine teeth, and the percentage of relative erosion resistance (%RER) was measured. After demineralizing them in a solution at a pH of 4.5 for 60 minutes, the enamel samples were treated with the respective solutions for 16 hours at a pH of 6.5. Acid exposure involved immersing the samples in 8 ml of citric acid solution for 1 hour at 37°C. The results indicated that chitosan hydrochloride at concentrations of 0.25% (-41.9±11.8; p<0.05) and 0.5% (-30.67±16.34; p<0.05) provided protection against acid erosion comparable to the positive control, fluoride (-44.44±15.89; p<0.05), while the result for deionized water was -91.25±30.01; p<0.05. To understand the mechanism, the ability of the compounds to adhere to the enamel surface was examined using a light microscope. Representative images of the enamel samples were captured before and after a single 3-minute application of the test compound, followed by immersion in deionized water three times and reimaging. The images showed that 0.2% chitosan hydrochloride remained on the sample surfaces. In conclusion, chitosan hydrochloride demonstrates potential as a vegan alternative to fluoride for enhancing acid resistance by adhering to the tooth surface.