The molecular catalyst Ru(bda)L2 (H2bda = 2,2′-bipyridine-6,6′-dicarboxylic acid, L = 6-bromophthalazine) shows excellent catalytic activity for water oxidation. By using Ce(NH4)2(NO3)6 as an oxidant, the catalyst reached a high turnover number TON = 100 000 in 3 hours.