Objectives: The aims of this research were to evaluate changes in ulcer size, pain reduction, satisfaction and side effects of 0.5% Acemannan for recurrent aphthous ulcers treatment when compared with 0.1% Triamcinolone acetonide. Materials and Methods: 52 volunteers with recurrent aphthous ulcers were randomly divided into 2 groups, with 26 volunteers per group. Medication was applied to the ulcer site 4 times/day for 7 days. Student’s t test was used to compare the difference between the two groups and repeated measure ANOVA was used to analyse the difference within group. p-value <0.05 was considered to be statistically significant. Results: There was no significant difference in ulcer size and pain reduction, as well as, satisfaction between subjects treated with 0.5% Acemannan and 0.1% Triamcinolone acetonide. No side effects were reported in both groups. Conclusion: 0.5% Acemannan and 0.1% Triamcinolone acetonide comparable efficacy in ulcer size reduction, pain reduction and satisfaction with no side effects in patients with recurrent aphthous ulcers. Therefore, 0.5% Acemannan can be an alternative treatment for oral aphthous ulcers.