In order to estimate their growth rates, high-resolution 10Be profiles of three manganese crusts have been measured using accelerator mass spectrometry. One crust from the Pacific Ocean (D96-m4) displays a constant growth rate from its upper to its lower surface. Applying the 10Be generation rate of 6.1±0.13 mm/Ma, we can estimate an age of about 6.8 Ma from the beginning of growth. The depth profile of 10Be in the other crust from the Pacific Ocean (D858) displays an identical "V" distribution pattern and an increase from the center towards the sides. Both sides were apparently simultaneously generated about 12.5 Ma ago. Applying the known 10Be generation rate, their growth rates are 3.5±0.7 and 1.4±0.3 mm/Ma, respectively. The crust from the Sea of Japan (004) displays a constant growth rate from the surface to a 9 mm thick upper zone. Applying a 10Be growth rate of 1.3±0.2 mm/Ma we estimate an age of about 6.9 Ma from the beginning of growth. The changes in growth rate before about 6.8 and 12.5 Ma seem to reflect changes in the paleo-oceanography.