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We studied the activity of osteoblastic cells on biphasic calcium phosphate (BCP) containing ca. 50 wt % hydroxyapatite and ca. 50 wt % ¢-tricalcium phosphate. The influence of the microtopography on the cellular activity was investigated by using three kinds of BCP scaffolds, which were composed of densely packed domains of 35 µm in size (dense-BCP), a porous framework of ³1 µm in width (micro-BCP), and aggregated particles of ³100 nm in diameter (nano-BCP). Basically, stable adhesion of the cells was achieved with defined focal adhesions on the BCP scaffolds regardless of their topography. The alkaline phosphatase (ALP) activity in the initial stage of the adhesion was more enhanced on micro-and nano-BCPs than it was on dense-BCPs due to the presence of a large number of calcium ions eluted from small grains in the micro-and nano-BCPs. However, the proliferation and the ALP activity were suppressed in the long-term culture on nano-BCP because of the limitation of the domain area for the formation of focal adhesions. Therefore, the cellular activity was successfully controlled with the surface microtopography of the scaffolds. The microstructured surface providing a sufficient domain area and essential ions would be suitable as a scaffold for osteoblastic cells.