The effect of polysaccharide fraction from oyster mushroom (POM) on texture, rheological and melting properties, density, water activity, colour, and antioxidative properties of acid casein model processed cheese was investigated. The samples were tested after 24 h and 21 days of cold storage. The hardness of cheeses with POM (0.125–0.25%) was lower than the control cheeses without POM. The oscillation rheology test indicated that the transition temperature (tan (δ) = 1) shifted as the POM content increased. The storage modulus (G′) was higher than the loss modulus (G″) during the experiment. The initial storage and loss moduli values were higher after the storage period, correlated with the higher hardness. Non-stored and stored samples had good meltability (Schreiber test number >4). The addition of POM increased antioxidant activity (FRAP). Considering good physicochemical and antioxidative properties, the optimal percentage of POM in processed cheese was 0.25%.