Cornhusk, corncob, and stigma maydis were extracted with water, aqueous ethanol, aqueous methanol, and ethyl acetate, respectively. The total phenolic contents (TPC), total flavonoid contents (TFC), total ketosteroid contents (TKC), and antioxidant activities [2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 2,2'-diphenyl-1-picrylhydrazyl (DPPH) and 2,4,6-tri(2-pyridyl)-1,3,5-triazine (TPTZ) radical-scavenging activity, reducing power, and ferric reducing-antioxidant power (FRAP)] of the above extracts were investigated. Their main antioxidant components were further determined and quantified by high performance liquid chromatography (HPLC). The results revealed that the aqueous ethanol and aqueous methanol were more efficient in extracting antioxidant constituents from cornhusk, corncob, and stigma maydis. Eight main antioxidant components were detected from above three by-products, and the contents of four main antioxidant components were determined. The present work revealed that the cornhusk and corncob showed similar high TPC, TFC, TKC, and antioxidant activities with stigma maydis, and could be used as potential candidates for the prevention of diseases related to various oxidant by-products of human metabolism.