Prince Joao of Portugal (June 3, 1537 - January 2, 1554) (in English: John) was the eighth son of King John III of Portugal by his wife Catherine of Habsburg, princess of Spain.

João was born in June 3, 1537 in Évora and became the heir to the throne of Portugal in 1539. He survived his four older brothers that died in childhood, but was a sickly teenager. The successive inter-marriages between the houses of Spain and Portugal had probably some responsibility on his ill health. In 1552 he married Joan of Habsburg, princess of Spain and his direct cousin, through both paternal and maternal line.

João died of what the sources refer to as consumption (tuberculosis) on January 2, 1554. Eighteen days later, a posthumous son was born from his marriage: the future king Sebastian I of Portugal. His death at the age of only sixteen was the beginning of the succession problem in Portugal that would end in the loss of independence to Spain in 1580.