3C 66B is an elliptical Fanaroff and Riley class 1 radio galaxy[2] located in the constellation Andromeda.

With an estimated redshift of 0.021258,[1] the galaxy is about 300 million light-years away.

[2] The orbital motion of 3C 66B showed supposed evidence for a supermassive black hole binary (SMBHB) with a period of 1.05 ± 0.03 years,[5] but this claim was later proven wrong (at 95% certainty).

[6] Messier 87 (M87), about 55 million light-years away, is the largest giant elliptical galaxy near the Earth, and also contains an active galactic nucleus.

[7] 3C 66B is an outlying member of Abell 347 which is part of the Perseus–Pisces Supercluster.