The objective of the present study was to prepare the phenolic-rich extract (PRE) from the mushroom (Agaricus bisporus) and investigate there in vitro antioxidant activity as well as estimation the contents of total phenolic and total flavonoids. The antibacterial activities against gram-positive and gram-negative bacteria were estimated. On the other hand, PRE from Agaricus bisporus was estimated as a bio-preservative article in Ultra filtered Feta-like cheese. In vitro study with DPPH-assay showed that the antioxidant activity of PRE increased gradually as concentration increases. The antibacterial activity of PRE increased with increasing the concentration of total phenolic compounds. This treatment was found to reduce the total bacterial, coliform, mold and yeast counts in feta like cheese compared with control. The score given for flavor increased gradually with advanced storage to be evaluated as extremely and like very much. It can be concluded that Mushroom (Agaricus bisporus) could be added as an additional nutrient to dairy products (UF-Feta like cheese) as it constitutes a new potential source of natural antioxidant and antibacterial agents. The potentiality of this PRE at the level of 100 µg/ml as a useful additive to improve the bacteriological quality and shelf life of the product could be recommended.