Background: Acne vulgaris is a common chronic disorder of the pilosebaceous unit. Topical therapy is the mainstay of treatment for mild-to-moderate acne. Two main problems with conventional anti-acne treatments are antibiotic resistance and local side effects. In this regard, medicinal herbs could be an alternative choice for developing new products with fewer side effects. Objective: The purpose of this study was to evaluate the safety and efficacy of a topical formulation of cinnamon in patients with facial acne. Method: In this open-label, assessor-blind, and uncontrolled clinical trial, 20 patients (18F/2M) with mild-to-moderate facial acne were treated with topical cinnamon gel twice-daily for eight weeks. The outcomes of acne lesion count, red fluorescence parameters and skin biophysical profile were evaluated at baseline, 4 th and 8 th week. For safety assessment, any adverse drug reaction was recorded during the study. Results: Two months after using cinnamon gel, there was a significant reduction in the total (47%, p=0.000), inflammatory (42%, p=0.026), and non-inflammatory (48%, p=0.002) lesion count. Also, the size of red fluorescence spots was significantly reduced (p ≤0.05). In skin biophysical measurement, there was a significant decrease in erythema (61.31 ± 68.25), sebum (31.05 ± 36.15), and hydration (10.05 ± 10.16), as well as a significant increase in pH (0.63 ± 0.75). Some patients experienced mild, transient erythema and burning immediately after applying the gel, but no serious side effects were reported. Conclusion: Our results suggest that topicalcinnamongel is efficient and safe for the treatment of mild-to-moderate facial acne. IRCT registration code: IRCT2016031126938N3