We report on the discovery of a blue arc north of the brightest galaxy (G1) in the cluster of galaxies Cl0302+1658. Extending over more than 10″ for a curvature radius larger than 1 arcmin, this arc A1 is the third straight arc discovered so far. A smaller arc A2 (8″ long) is embedded in the southern envelope of G1, but is certainly not a counter arc of A1. A somewhat bluer and fainter arclet lies close to the A1 western end. The B-R and R-I color indices of A1 indicate that its redshift is likely to range around z=0.8, while the shape and the higher surface brightness of A2 point to a lower redshift. We give the B, R and I photometry of a sample of 36 galaxies in the cluster center, complete to the limiting magnitude B=25.