204 Kallisto is a fairly typical, although sizeable Main belt asteroid.

Like other asteroids of its type, it is light in colour.

It was discovered by Johann Palisa on 8 October 1879, in Pola, and was named after the same nymph Callisto in Greek mythology as Jupiter's moon Callisto.

Photometric measurements during 2009 produced a lightcurve that indicated a sidereal rotation period of 19.489±0.002 h with a variation amplitude of 0.18±0.02 magnitudes.

This result conflicted with previous determinations of the period, so the latter were ruled out.