Several strontium-incorporated nonstoichiometric hydroxyapatites with different contents of strontium were synthesized with a hydration process. Their phase structures, chemical compositions and grain sizes and morphologies were investigated by using XRD, FTIR and TEM to study their thermal ability at various firing temperatures. Results show that the incorporation of strontium into hydroxyapatite crystal by replacing equivalent calcium decreases its thermal stability under a given hydration condition and a same moral ratio of (Ca+Sr)/P. The decomposed product is the mixed calcium strontium phosphate ((Ca, Sr)3(PO4)2), whose decomposing temperature is lower than that of pure tricalcium phosphate. The more the content of strontium in place of calcium in hydroxyapatite is, the larger the amount of strontium incorporated into the crystal lattice of tricalcium strontium phosphate is. At elevated firing temperatures, the grains of strontium-incorporated hydroxyapatites and pure hydroxyapatite grow up gradually. However, below 1200 ℃, the grains of the former hydroxyapatite basically keep an equi-axed SrHA while those of the latter become irregular. At 1300 ℃, both hydroxyapatites are mainly composed of larger grains and few of small ones. The former is a grown apatite with irregular morphology and the latter is a decomposed mixed calcium phosphate or tricalcium strontium phosphate with spheric morphology.