Methanolic (MeOH) extract and crude polysaccharides of Plumeria alba leaves were evaluated for in vitro antioxidant activity. HPLC analysis for the MeOH extract revealed the presence of ten flavonoids and nine phenolic compounds with higher antioxidant capacity. Total phenolic compounds and total flavonoids were determined. The monosaccharide composition was performed on a Dionex system (Dx-120) ion chromatography. The detected polysaccharides are heteropolysaccharides, glucose and mannose were occupied the highest level followed by galactose and rhamnose. Additionally, Plumeria alba polysaccharides (PAPs) consisted of the protein-bound polysaccharide. Furthermore, 14 amino acids (Asp, Thr, Glu, Ser, Ala, Gly, Arg, Tyr, Cys, Ile, Lys, Val, Pro and Phe) were identified to be components of the protein-bound polysaccharide analyzed by automated amino acid analyzer. Antioxidant activity was evaluated at different concentrations ranged from 0.25 to 3 mg/ml using three different in vitro antioxidant activity assays. The obtained results clearly indicated that the MeOH extract and PAPs showed a strong antioxidant activity in terms of FRAP, DPPH^• free radical scavenging and reducing power assay. Thus, Plumeria alba could be a new source of natural antioxidants for functional foods or medicine due to its higher antioxidant potential, flavonoids and phenolics contents.