A study on the morphological changes of nanostructured hydroxyapatite in presence of polyethylene glycol synthesized by sol-gel technique is presented. Equimolar solutions of Ca(NO3)2·4H2O and (NH4)2HPO4 dissolved in ethanol were used in the synthesis at 85 °C. Polyethylene glycol is added as an organic modifier. The product was sintered at 400,750 and 1100°C. The XRD and FTIR results indicated the presence of amorphous hydroxyapatite in as dried gel precursor and single phase HAP was obtained after heat treatment at 1100°C at 4 h. SEM images of the precursor appear agglomerated leaving sub micrometric pores between them and the small particles seen embedded in each agglomerated cluster with an average diameter of 50-70 nm. At high temperatures the more flexible polyethylene glycol molecules induced the orientation growth which leads to the formation of HAP platelets. © 2010 Elsevier B.V. All rights reserved.