Genetic differentiation and antioxidant activities in ethanolic extracts from leaves of Bouea macrophylla Griffith were determined. The result revealed genetic differentiation among sour ma-praang, ma-yong and sweet ma-praang of B. macrophylla Griffith (φ PT =0.772, p-value=0.000). In addition, high genetic diversities were found in sour ma-praang and sweet ma-praang populations (P: 51.4 and 57.1 %; He: 0.1900.035 and 0.2240.036, respectively), but low genetic diversity was found in ma-yong population (P: 8.6 %; He: 0.0350.021). Total phenolic contents of sour ma-praang, ma-yong and sweet ma-praang were estimated as 680.51±89.81, 701.03±59.89 and 530.85±41.23 mg gallic acid/g extract, respectively. Free radical scavenging activities of sour mapraang, ma-yong and sweet ma-praang were found (1/EC50= 4.17, 1.43 and 1.37, respectively) corresponding with metalchelating activities (1/EC50=0.83, 0.65 and 0.17, respectively). Therefore, the obtained data may be applied to cultivation and utilization of their leaves as source of natural phenolics and antioxidants.