Giacomo Rho SJ (1593, Milan – 27 April 1638, Beijing) was an Italian Jesuit missionary in China.
Rho, the son of a jurist, entered the Society of Jesus at the age of twenty.
During the siege of that city by Dutch forces in 1622, he was attributed by Jesuit sources to be the one who fired a cannon shot that landed on a barrel of gunpowder in the midst of the Dutch formation, which turned the tide of the battle and saved the city from the attack.
Together with Johann Adam Schall von Bell, he occupied himself on this task until the end of his life seven years later, in 1638.
Rho left works relative to the correction of the Chinese calendar and other astronomical and theological questions.