The aim of this study was to evaluate the antioxidative compositions, capacity and functions of Night-blooming Gereus (fruits of Hylocereus undatus and polyrhizus). The antioxidative compositions including polyphenols, flavonoids, anthocyans, carotenoids, tannins and porphyrins were determinated. The inhibition of conjugated dienes formation in linoleic acid emulsion autoxidation system was determined as antioxidative capacity. The antioxidative functions, such as reducing power, scavenging activity of DPPH radical, chelating effect with Fe(superscript 2+) ion and scavenging activity of superoxide anion, were determined. In results, H. polyrhizus had significantly higher flavonoids, anthocyans, carotenoids and porphyrins contents as compared to H. undatus. The content of polyphenols and tannins between two cultivars had no differences. H. polyrhizus had better inhibition percentage of conjugated dienes formation at 2.5 mg/mL in methanol extracts. The antioxidative functions, such as reducing power and scavenging effect of DPPH radicals were significantly higher in H. polyrhizus while there was no difference between two cultivars in chelating effect with Fe(superscript 2+) ion. Both cultivars had lower scavenging effect of superoxide anion.