Fibrous hydroxyapatite ( HA ) was grown upwards from the crosslinked unsaturated polyphosphoester( UPPE ) which was used as an injectable bone tissue engineering scaffolds. Composition of fibrous HA was determined by FT- IR, XRD and EDX, which suggested that the fibrous HA was calcium deficient carbonated apatite with low crystallinity. SEM micrographs indicated that the fibrous HA had a hollow tubing structure and tube wall was a flakelike assembly. The fibre with poor mechanical property and with a growth rate about 0.5mm/min reached several centimeters in length after 2 hours . The growth was at the tip of the fibre suggested that the procedure of forming fibrous HA was as follows: Ca2 + ions were firstly incorporated into the crosslinked UPPE by dipping in Ca2 + solution, then supplied through micropores of the material reacted with PO3- 4 ions to form a small tube, the osmotic pressure or capillary force lead the Ca2 + continuously gushed out into the PO 3- 4 solution,thus fibrous HA was obtained.