Osteoblasts (MC3T3-E1) were cultured on polysaccharide type polyelectrolyte complex (PEC). The growth of the MC3T3-E1 on the PEC with carbxyl group (c-type) was slightly suppressed and exhibited aggregation morphology. On the other hand, cell growth on the PEC with sulfate group (s-type) was enhanced and the cell exhibited spreading form. Differentiation markers of osteoblast (ALPase activity, calcification, expression of osteocalsin) were enhanced and localized around cell aggregates on c-type PECs. These results suggest that PEC has the ability to control osteoblast proliferation and differentiation.