ABSTRAK Jamur tiram (Pleurotus ostreatus) merupakan jenis jamur yang dapat dikonsumsi dan memiliki aktivitas sebagai antioksidan. Penelitian ini bertujuan untuk menentukan aktivitas antioksidan dari ekstrak metanol jamur tiram yang dibudidaya di Aceh. Jamur tiram diekstraksi menggunakan metode maserasi menghasilkan ekstrak kental dengan rendemen 8,52 g ekstrak/100 g sampel kering. Hasil karakterisasi ekstrak metanol jamur tiram diperoleh kadar air, kadar abu total, kadar sari larut air, dan kadar sari larut etanol berturut-turut 18,48%; 7,29%; 53,23%; dan 61,92%. Hasil uji fitokimia menunjukkan ekstrak metanol jamur tiram mengandung saponin, alkaloid, steroid, flavonoid, dan glikosida. Aktivitas antioksidan dengan metode ABTS (2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)) menunjukkan bahwa ekstrak metanol jamur tiram memiliki aktivitas antioksidan yang kuat dengan IC50 58,50 µg/ml. Kata kunci : Jamur tiram, ekstrak metanol, metode ABTS, IC50, antioksidan. ABSTRACT Oyster mushroom (Pleurotus ostreatus) is edible mashroom that has antioxidant activity. The study aims to determine antioxidant activity of Oyster mushroom methanol extract that was cultivated in Aceh. Oyster mushroom was extracted by using maceration method yielded concentrated extract 8,52 g extract/100 g dry sample. Characterization result of Oyster mushroom methanol extract contain 18,48%; 7,29%; 53,23%; and 61,92% of water, total ash, water soluble extract and ethanol soluble extract respectively. Phytochemical assay had showed that oyster mushroom methanol extract contains saponins, alkaloids, steroids, flavonoids and glycosides. Antioxidant activity was measured by ABTS (2,2 Azinobis (3-ethylbenzothiazoline)-6-sulfonic acid) method, the result showed that methanol extract of Oyster mushroom has a strong antioxidant activity with IC50 58.50 µg/ml. Keyword : Oyster mushroom, methanol extract, ABTS method, IC50, antioxidant.