Nils Gabriel Sefström (2 June 1787 – 30 November 1845) was a Swedish chemist. Sefström was a student of Berzelius and, when studying the brittleness of steel in 1830, he rediscovered a new chemical element, to which he gave the name vanadium.
Vanadium was first discovered by the Spanish-Mexican mineralogist Andrés Manuel del Río in 1801. He named it erythronium. Friedrich Wöhler later confirmed that vanadium and erythronium were the same substance.
Sefström was member of the Royal Swedish Academy of Sciences from 1815.
The Spitzbergen glacier Sefströmbreen, and the mountain ridge of Sefströmkammen, are named after him.