Duke Pius August in Bavaria, full German name: Pius August Herzog in Bayern (born 1 August 1786 in Landshut, Electorate of Bavaria; died 3 August 1837 in Bayreuth, Kingdom of Bavaria) was a Duke in Bavaria as a member of the Palatine Birkenfeld-Gelnhausen line of the House of Wittelsbach.
Pius August was a grandfather of Empress Elisabeth of Austria through his son Duke Maximilian Joseph in Bavaria, as well as a great grandfather of Queen Elisabeth of the Belgians and an ancestor of the current generations of the Belgian and Italian Royal Families and the Grand Ducal Family of Luxembourg .