Orthosie (or-thoh'-see-a) is a natural satellite of Jupiter. It was discovered by a team of astronomers from the University of Hawaii led by Scott Sheppard, et al. in 2001, and given the temporary designation S/2001 J 9. Orthosie is about 2 kilometers in diameter, and orbits Jupiter at an average of 20,721,000 kilometers. It is also designated as Jupiter XXXV.

It is named after Orthosie, the goddess of prosperity and one of the Horae. The Horae (Hours) were daughters of Zeus and Themis.

It belongs to the Ananke group, retrograde irregular moons which orbit Jupiter between 19.3 and 22.7 Gm, at inclinations of roughly 150°.