Segue 3 is extremely faint—its visible absolute magnitude is estimated at −1.2 or even at about 0.0 ± 0.8, which means that the cluster is only 100 to 250 times brighter than the Sun. Its small radius—of about 2.1 pc—is typical for the galactic globular clusters. The cluster has a slightly flattened shape and shows some evidence of the tidal disruption.
The metallicity of Segue's 3 stars is [Fe/H] ≈ −1.7, which means that they contain 70 times less heavy elements than the Sun. These stars are more than 12 billion year old. Segue 3 appears to be one of the faintest globular clusters of the Milky Way.