A new long chain fatty alcohol acetate identified as 17-hydroxypentacosanyl acetate (1), together with a new xanthone identified as 1,8-dihydroxy-3,6-dimethoxy-xanthone-5-O-[-L-rhamnopyranosyl-(1"2')]--D-glycopyranoside (3), as well as two new lignans identified as (+)-lyoniresinol-3a-O-[-L-rhamnopyranosyl-(1"'6")]--D-glucopyranoside (4) and (+)-isolariciresinol-3a-O-[-L-rhamnopyranosyl-(1"'2")--L-rhamnopyranosyl-(1""6")--D-glucopyranoside (5), in addition to -sitosterol-3-O-acetate (2) were isolated from the methanolic extract of the aerial parts of Polygonum bellardii growing in Egypt. Their structures were elucidated on the basis of different chemical and spectroscopic evidences. The total extract and its fractions, in addition to compounds (3, 4 and 5) showed significant antioxidant potential by DPPH• scavenging activity technique.