Abstract　Collagen　mimetic　peptide-PEG　hybrid　hydrogels　have　emerged　as　a　new　class　of　synthetic　collagen　mimics　with　well-defined　structure　and　composition.　Herein,　we　probed　the　versatility　of　a　collagen　mimetic　peptide-PEG　hybrid　hydrogel　for　biomimetic　synthesis　of　hydroxyapatite.　This　was　achieved　by　double-diffusion,　where　ion　precursors　diffused　from　opposite　directions　into　the　hydrogel　to　form　a　precipitant　band　with　hydroxyapatite　minerals.　Morphological　and　crystallographic　analyses　revealed　these　minerals　adopted　platelet-shaped　morphology　with　cobble-like　subunits　of　mesoscopic　size　and　exhibited　single　crystal-like　scattering　patterns,　which　was　characteristic　of　mesocrystals.　The　gel-mediated　strategy　in　our　study　may　be　applicable　to　study　mechanisms　concerning　hydroxyapatite　mesocrystals　formation　and　to　construct　functional　materials.　©　2015　Elsevier　B.V.