Apatite-coated bio-inert implants can provide well-behaved bone substitutes in bioactive and mechanical properties. In this work, citric acid (CiA) was added into a dipping solution of 1.67Ca(NO 3 ) 2 -PO(OH) x (OEt) 3 - x to investigate its effect on wettability, apatite formation, and film morphology. The dipping solution with a CiA/Ca ratio of 0.5 led to a good wettability on alumina substrates, formation of oxy-hydroxyapatite phase in the film after 800 o C heat treatment, rough or porous surface morphology, and adhesive strength up to 10MPa. CiA in the dipping solution has a strong gelation ability and gives rise to corresponding changes in the film.