Chitosan-GPTMS (γ-Glycidoxypropyltrimethoxysilane) hybrid hydrogels were synthesized with β-glycerophosphate (β-GP) as the additive agent. Chitosan-GPTMS sols were fluid at room temperature and transformed to hydrogel at 36.5°C in several min. The gelation time of the hydrogels was shortened by the addition of GPTMS. From NMR experiments, this gelation behavior depended on some factors, namely, electrostatic interaction between the phosphate groups of β-GP and the amino groups of chitosan chains, crosslinking between the epoxy groups of GPTMS and the amino groups of chitosan, and polycondensation of the methoxy groups of GPTMS. The Si(IV) released from the hydrogels promoted the cell adhesion and ALP activity of osteoblastic cells MG63.