Biodegradable inorganic-organic composite hollow spheres, consisting of poly L-lactic acid , calcium carbonate, b-tricalcium phosphate and siloxane, were prepared by an oil-in-water emulsion evaporation method to develop an injectable bone substitutes incorporated with cells. The spheres had an almost flat diameter of about 1.0 mm and an open channel of 500-600 mm in diameter on the shell. After soaking the spheres in a simulated body fluid, the silicon and calcium ion-species were gradually released from the spheres. Osteoblast-like cells, marrow stromal cells MSCs and osteoblasts migrated into the spheres through the open channel and attached to the inside surface of the sphere shell. The MSCs expressed a high level of alkaline phosphatase on the spheres. Some bone nodules formed on the spheres after the culture of osteoblasts.