An oxidation catalyst is described for treating an exhaust gas produced by a diesel engine comprising a catalytic region and a substrate, wherein the catalytic region comprises a catalytic material comprising: bismuth (Bi), antimony (Sb) or an oxide thereof; a platinum group metal (PGM) selected from the group consisting of (i) platinum (Pt), (ii) palladium (Pd) and (iii) platinum (Pt) and palladium (Pd); and a support material, which is a refractory oxide; wherein the platinum group metal (PGM) is supported on the support material; and wherein the bismuth (Bi), antimony (Sb) or an oxide thereof is supported on the support material and/or the refractory oxide comprises the bismuth, antimony or an oxide thereof.