Johann Ernst of Saxe-Weimar (German: Johann Ernst von Sachsen-Weimar) (25 December 1696 – 1 August 1715) was a German prince, son by his second marriage of Johann Ernst III, Duke of Saxe-Weimar. Despite his early death he is remembered as a collector and commissioner of music and as a composer, some of whose concertos were arranged for harpsichord or organ by Johann Sebastian Bach, who was court organist in Weimar at the time.