John Ernest (German: Johann Ernst) (10 May 1521 – 8 February 1553) was a Duke of Saxe-Coburg and a member of the House of Wettin.

After the death of his father (1532), his half-brother, John Frederick I, became Elector of Saxony.

However, it was not until Battle of Mühlberg in 1547, in which the elder brother was captured by Emperor Charles V, that John Ernest could govern undisturbed in Coburg.

After his death in Coburg, the city fell for a few months to John Frederick — released from the imperial detention — before his death, and then, to his three sons, which governed the Ernestine lands together from 1554 for some years.

His widow later married Philip II, Count of Schwarzburg-Leutenberg.