Friedrich Paul Georg Nikolaus von Sachsen-Altenburg) (16 September 1826 in Hildburghausen – 7 February 1908 in Altenburg), was a duke of Saxe-Altenburg.
He was the first son of Georg, Duke of Saxe-Altenburg and Marie Luise of Mecklenburg-Schwerin.
In 1853 he succeeded his father as Duke of Saxe-Altenburg.
He was of a retiring disposition and he took little active part in running the country.
After a reign that lasted fifty five years, he died without a living direct male heir; because of this, he was succeeded by his nephew, Ernst.