Present study was designed to compared the total flavonoids and polyphenols contents and antibacterial activity of hawthorn extracts with different polarities as well as the underlying antibacterial mechanisms. The results showed that among all hawthorn extracts, methanol and ethanol extracts (ME and EE) exhibited high levels of total flavonoids and polyphenols contents, followed by acetone, ethyl acetate, trichloromethane and petroleum ether extracts. ME exhibited the strongest antibacterial activity against tested bacteria, especially Staphylococcus aureus with a 1.25 μg/mL of the minimum inhibitory concentration (MIC) and minimum bactericide concentration (MBC). Further analysis revealed that the main phenolic compounds from ME were epicatechin (281.6 mg/100 g DW), procyanidin B2 (243.5 mg/100 g DW), chlorogenic acid (84.2 mg/100 g DW) and quercetin (78.4 mg/100 g DW). The action mechanism of ME against S. aureus could be ascribed to ME damaging cell wall and cell membrane integrity, inhibiting intracellular enzyme activity, increasing reactive oxygen species (ROS), also changing expression of associated genes and then inducing apoptosis of S. aureus. in addition, the antimicrobial activity of ME against S. aureus has also been demonstrated to be efficient in the food matrix (whole milk). Crataegus pinnatifida Bge. (Rosaceae), informally called hawthorn tree, is a widely cultivated perennial woody plant in China 1. Hawthorn has an extremely long edible history and also a well-known Chinese herbal medicine 2. Hawthorn is rich in carbohydrate, organic acids, vitamins and mineral elements 3 , but also has a range of diverse biological functions including antioxidant, antibacterial effect and pharmacological effects on digestive, cardiovascular and endocrine systems, neuroprotective function and preventing obesity 4-7. Polyphenols have been recognized as one of mainly bioactive compounds in hawthorn, and it contained more than 150 phenolic compounds including procyanidins (procyanidin B2, procyanidin B5 and procyanidin C1), flavonoids (epicatechin, hyperoside, quercetin, rutin and isoquercitrin), and triterpenoids acid (ursolic acid, corosolic acid, oleanolic acid and maslinic acid) 8. Traditionally, hawthorn fruits are consumed directly or processed into jams, jellies, wine, juice and various sweet foods 9. Now, with the booming of functional and health care industry, hawthorn extracts as a kind of nutrient enhancer have been widely used 10,11. Wen et al. studied phenolic contents and cellular antioxidant activity of 80% acetone extracts from three varieties of hawthorn 6. Zhang et al. found the ethyl acetate extracts were only effective in inhibition of LDL oxidation among examined four different solvents 12. Miao et al. studied the antioxidant activity, chemical compositions of hawthorn extracts obtained using different solvents, the results showed that the highest total flavonoids and total polyphenols was obtained from 80% acetone extract, but the deionised water extract has the best DPPH scavenge capacity an...