Wild and cultured mushrooms have been extensively used for food and medicinal purposes all around the world. However, there is limited information on chemical composition, health enhancing effects and contributions on diet of some mushrooms (e.g., Agaricus arvensis) widely distributed in many countries including United Kingdom, Australia, Turkey etc. Therefore, the present study was aimed to analyse the bioactive composition and ameliorative effects of A. arvensis via evaluating in vitro and in vivo antioxidant properties in CCl4 induced rat model. The extract exhibited higher antioxidant capacities in vitro than that of the positive control (Reishi-Shiitake-Maitake standardized extract). Administration of the extract had significant regulative effects in the levels of AST, ALT, LDH, Urea and TRIG levels according to CCl4 group. Additionally, lipid peroxidation and GSH in the brain, kidney and liver tissues was regulated by extract treated groups compared to the CCI4 group. The supplementation of the extract at the dose of 100 mg/kg regulated the levels of GST, GR, CAT and GPx enzyme activities in brain and liver, but not in kidney tissue. There was approximately three fold increase in CAT enzyme activity in kidney tissue of extract treated groups compared to Control and CCl4 groups. The extract contained a rich composition of bioactive compounds including phenolics (protocatechuic acid and p-hydroxybenzoic acid), volatile compounds (benzaldehyde, palmitic acid and linoleic acid) and mineral compounds (K, Si, Mg and Na). Data obtained within this study suggests that A. arvensis might be used for food industries in order to obtain nutritional products.