Prince Nikolaus August of Sweden and Norway, Duke of Dalarna (24 August 1831 – 4 March 1873) was the youngest of the five children of King Oscar I of Sweden and Josephine of Leuchtenberg.

Born in Drottningholm Palace in Ekerö, , his eldest sibling was King Carl XV of Sweden.

During parts of 1849-1853, he was a student at Uppsala University. On 10 December 1851, he was made an honorary member of the Royal Swedish Academy of Sciences.

On 16 April 1864 in Altenburg, the Duke married Princess Therese Amalie of Saxe-Altenburg (Ansbach, 21 December 1836 - Haga Palace, , 9 November 1914), Duchess of Saxony, eldest daughter of Prince Eduard of Saxe-Altenburg. The marriage did not produce issue. In Sweden, his wife was styled Princess Teresia.

The Prince was very interested in trains and locomotives, and a locomotive was named after him. Since it was commonly thought the Prince was not very bright, this led to the expression "dummare än tåget" (lit. "more stupid than the train"), an expression still in use in the Swedish language.

Prince August died at the age of 41 of pneumonia at the , .

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