Abstract: Two biological aerated filter (BAF) reactors using different fillings, separately, i.e. ceramic pellets (CPs) and granular active carbon (GAC), were built and used to remove geosmin and 2-MIB from water. Further, their start-up characteristics were investigated by comparing odorant removal efficiencies and start-up time. At the same influent water, the two BAFs were quite similar in dissolved organic carbon (DOC) removal efficiency and both removal rates stabilized over 70% in 24 days. However, the two BAFs differed significantly in start-up time for removing geosmin and 2-MIB, separately, i.e. 30 and 26 days respectively in CPs-BAF and 62 and 43 days respectively in GAC-BAF. Moreover, the geosmin removal rates in GAC-BAF and CPs-BAF were stable at about 95% and 69%, respectively, and the rate and stability for geosmin removal of the former was obviously higher than of the latter. And the removal rates of 2-MIB in GAC-BAF and CPs-BAF were similar to each other and stable at about 75% and 73%, respectively, but the stability of the former was higher than of the latter.