We present the results of B, V, R surface photometry of ESO 603-G21 - a galaxy with a possible polar ring. The morphological and photometric features of this galaxy are discussed. The central round object of the galaxy is rather red and presents a nearly exponential surface brightness distribution. This central structure is surrounded by a blue warped ring or disk. The totality of the observed characteristics (optical and NIR colors, strong color gradients, HI and H(2) content, FIR luminosity and star-formation rate, rotation-curve shape, global mass-to-luminosity ratio, the agreement with the Tully-Fisher relation, etc.) shows that ESO 603-G21 is similar to late-type spiral galaxies. We suppose that morphological peculiarities and the possible existence of two large-scale kinematically-decoupled subsystems in ESO 603-G21 can be explained as being a result of dissipative merging of two spiral galaxies or as a consequence of a companion accretion onto a pre-existing spiral host.