Peter II, Grand Duke of Oldenburg (German: Nikolaus Friedrich Peter) (8 July 1827–13 June 1900) was the Grand Duke of Oldenburg from 1853 to 1900. He claimed hereditary parts of Duchy of Holstein after the Second Schleswig War in 1864. After signing a treaty on 23 February 1867 in Kiel, he renounced his claims. But, he received the district of Ahrensbök, the Prussian parts of the former Principality of Lübeck (except the village of Travenhorst), and was given a million taler as compensation from Prussia. Thus the Grand Duchy of Oldenburg gained access to the Baltic Sea.

Duke Nikolaus Friedrich Peter was the only son of Augustus, Grand Duke of Oldenburg by his second wife Princess Ida of Anhalt-Bernburg-Schaumburg-Hoym. He was born on 8 July 1827 in Oldenburg.

In his youth, he served as a General of Cavalry in the Prussian army. He also served as General of Infantry in the Hanoverian army.

On 10 February 1852, Peter married Princess Elisabeth of Saxe-Altenburg. She was the fourth daughter of Joseph, Duke of Saxe-Altenburg and Amelia of Württemberg, and was a sister of Queen Marie of Hanover and Grand Duchess Alexandra Iosifovna of Russia.

They had two sons, Frederick Augustus (born in 1852) and George (born in 1855). Peter II may have had an illegitimate son, Peter Altmann (Rastede 1857-Brighton 1934), married and had issue.

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