Abstract: The Diyanmiao ophiolite, consisting of serpentinized enstenite pyrolite, gabbro, basalt and spilite-keratophyre, is situated in the Daxinganling-Mongolia orogenic belt between Sino-Korean paleo-plate and Siberia paleo-plate. Petrographical study shows that the Diyanmiao gabbro can be classified into bedded gabbro (with cumulatic texture)and isotropic gabbro (with gabbro texture), both of which experienced low-medium metamorphic reformation. On the basis of field survey and study of geology, petrography and lithochemistry, the Diyanmiao gabbro is believed to form in a smallscaled monocycle closed system under the active continental margin or island arc.