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Beer is a fermented beverage rich in bioactive substances. The polyphenols and melanoidins and antioxidant properties were investigated in different commercial beers from China. Among all beer samples, total phenolic content (TPC) and total flavonoid content (TFC) were 14.81–53.39 mg GAE/100 mL and 9.46–44.72 mg RE/100 mL, respectively, with dark beer showing the highest TPC and TFC. 2,2’-azino-bis (3-ethylbenzthiazoline)-6-sulfonic acid (ABTS) (6.40 ± 0.13 mmol TEAC/L) and ferric reducing antioxidant power (FRAP) (2.61 ± 0.08 mmol TEAC/L) detected the highest antioxidant activity in dark beer. TPC and TFC were significantly correlated with antioxidant activity of beer, and TPC and TFC in high molecular weight (HMW) part were higher than those in low molecular weight (LMW), especially in dark beer. Furthermore, there were 15 phenolic compounds in HMW and 29 phenolic compounds in LMW. The relative contents of these phenolic compounds in LMW and HMW parts were 1.053 and 0.933 mg/mL, respectively. The highest Kmix 420 nmof HMW in dark beer was 0.224 ± 0.011 L/cm/g by spectroscopy. By size exclusion chromatography(SEC), dark beer HMW exhibited the higher molecular weight distribution than India pale ale HMW at 420 nm. HMW parts of dark beer exhibited flake structure by scanning electron microscopy (SEM), which had more holes and crystal-like particles than LMW fraction. Taken together, different molecular weight parts and beer samples showed various polyphenols and melanoidins profiles, which could provide guides for the antioxidant and healthy properties of different commercial beers.