Iota Horologii b (ι Hor b / ι Horologii b), often catalogued HR 810 b, is an extrasolar planet approximately 56.5 light-years away in the constellation of Horologium (the Pendulum Clock).

[2] The discovery of Iota Horologii b was the result of a long-term survey of forty Solar analog stars that was begun in November 1992.

The planet represents the first discovery of an extrasolar planet with a European Southern Observatory instrument, with the data found at the La Silla Observatory in Chile.

[1] The measurements of Iota Horologii show that the planet orbits the star approximately every 320 days.

Preliminary astrometric analysis of Iota Horologii b suggested that planet b may have as much as 24 times the mass of Jupiter with an inclination of 5.5 degrees from Earth's line of sight.