Extraction of the phenolic compounds, cinnamic and benzoic acid derivates, from Cinnamonum cassia (Nees & T.Nees) J.Presl was carried out. Classical solvent extraction, ultrasonication, maceration, and shaking methods were compared. Phenolic compounds were identified based on ultrahigh-performance liquid chromatography with photodiode array detector. The optimum solvent percentage was 60% (v/v) ethanol (EtOH) in a ratio of 1:20 with the cinnamon sample weight. The optimum extraction time was 90 min, and the optimum extraction temperature was 50 o C. Under optimized conditions, the highest phenolic contents were 2.263±0.089 mg/g of free acids for sinapic acid, and the contents of cinnamic acid were 0.103±0.031 mg/g of free acids. The antioxidant capacity of the extract produced using the best extraction conditions was 14.337±4.662 mmol/g and the total phenolic content was 1.918±0.528 mmol/g.