Context: Acne is an inflammatory disease of the sebaceous glands that results in the formation of papules, pustules, and more advanced complicated scars by opportunistic micro-organisms that are known as Propionibacterium acnes which feed mainly on fat. The need to reduce the use of antibiotics and the discovery of medicinal plant treatments, due to the resistance of Bacteria over time. Propionibacterium acnes is a gram-positive bacterium that plays the main role in the development of some diseases. Aims: This study aimed to investigate the effect of Alginin which was extracted from Pleurotus ostreatus fungus on Propionibacterium acnes. Method: The study involved (100) samples, which were collected from 75 patients suffering from acne, 65 samples of comedones, and 35 pustules, ages ranging between (14-20) years. All samples were collected from adolescent patients in Mosul City/Iraq. All samples indicated the presence of P. acne. Results: A marked effect was observed through the inhibition of the growth of Propionibacterium acnes as the diameter of inhibition of the extract of Alginin ranged between 9.5 mm to 11.5 mm. So, we suggest the possibility of using Alginin as an alternative to antibiotics in the treatment of skin affected by acne.