三氧化二镍，化学式Ni₂O₃。

灰黑色无气味有光泽的块状物，易碎成细粉末。不溶于水，溶于氨水。溶于热盐酸并放出氯气。溶于硫酸和硝酸并放出氧气。600°C分解为一氧化镍和氧气。

Nickel(III) oxide is the inorganic compound with the formula Ni₂O₃. It is not a well characterised, sometimes referred to as black nickel oxide. Traces of Ni₂O₃ on nickel surfaces have been mentioned. A related, better characterized material is nickel oxide hydroxide (NiOOH), which is likely the reagent employed in organic synthesis since it is generated in aqueous media.