NGC 3521 is a flocculent[4] intermediate spiral galaxy located in the constellation Leo.

Its velocity with respect to the cosmic microwave background is 1167 ± 26 km/s, which corresponds to a Hubble distance of 56.1 ± 4.1 Mly (17.21 ± 1.26 Mpc).

[6] NGC 3521 has a morphological classification of SAB(rs)bc,[2] which indicates that it is a spiral galaxy with a trace of a bar structure (SAB), a weak inner ring (rs), and moderate to loosely wound arm structure (bc).

[7] The bar structure is difficult to discern, both because it has a low ellipticity and the galaxy is at a high inclination[2] of 72.7° to the line of sight.

[9] Astronomers originally classified it as type IIb, but spectroscopy suggests this supernova is very similar to SN 1994I.