54 Piscium b (HD 3651 b), occasionally catalogued as 54 Piscium Ab to differentiate from the brown dwarf in the system, is an extrasolar planet[3][1] approximately 36 light-years away[4] in the constellation of Pisces.

On January 16, 2003, a team of astronomers (led by Geoff Marcy) announced the discovery of an extrasolar planet around 54 Piscium using the radial velocity method,[1] a process utilizing the "wobbling" effect that a star may experience if something is tugging on it.

The highly elliptical orbit, however, suggested that the gravity of an unseen object farther away from the star was pulling the planet outward.

The eccentric orbit became clear with the discovery of the brown dwarf within the system.

In a 2006 simulation with the brown dwarf, 54 Piscium b's orbit "sweeps clean" most test particles within 0.5 AU, leaving only asteroids "in low-eccentricity orbits near the known planet’s apastron distance, near the 1:2 mean-motion resonance".