NGC 4603 is a spiral galaxy located about 107 million light years away in the constellation Centaurus. It is a member of the Centaurus Cluster of galaxies, belonging to the section designated "Cen30". The morphological classification is SA(s)c, which indicates it is a pure spiral galaxy with relatively loosely wound arms.
During 1999, this galaxy was the subject of an extended study using the Hubble Space Telescope to locate Cepheid variable stars. A total of were found, and the measurement of their periodicity gave a net distance estimate of . This is consistent with the distance estimate determined through redshift measurements. As of the time of this study, NGC 4603 was the most distant galaxy for which a distance estimate had been made using Cepheid variable.
On May 21, 2008, supernova SN 2008cn was discovered at a position 23.″2 north and 4.″7 east of the galaxy center. It was determined to be a high-luminosity Type II-P supernova, with a progenitor tentatively identified as a red supergiant with 15 ± 2 solar masses. Based upon the yellowish color, it may have been a member of a binary star system.