The　application　of　hydroxyapatite　(HAP)　in　different　fields　depends　greatly　on　its　morphology,　composition　and　structure.　Besides,　the　main　inorganic　building　blocks　of　human　bones　and　teeth　are　also　HAP.　Therefore,　accurate　shape　and　aggregation　control　and　of　hydroxyapatite　particles　will　be　of　great　interest.　Herein,　oriented　bundles　of　flowerlike　HAP　nanorods　were　successfully　prepared　through　hydrothermal　treatment　without　acid-base　regulation,　with　the　mono-alkyl　phosphate　(MAP)　and　sodium　citrate　as　surfactant　and　chelating　agent,　respectively.　The　prepared　samples　were　characterized　by　the　X-ray　diffraction　(XRD),　Fourier　transform　infrared　spectroscopy　(FTIR),　field　emission　scanning　electron　microscopy　(FESEM),　transmission　electron　microscopy　(TEM),　high-resolution　transmission　electron　microscopy　(HRTEM)　and　zeta　potential,　the　pH　value　and　conductivity　value　of　suspension　were　characterized　by　pH　meter　and　conductivity　measurement.　The　results　showed　that　the　MAP　and　citrate　play　an　important　role　in　assembly　of　HAP　nanorods　without　acid-base　regulation.　Citrate　calcium　complex　could　decompose　slowly　and　release　citrate　ions　at　hydrothermal　conditions.　Besides,　the　further　decomposition　of　citrate　ions　could　release　aconitic　acid　as　the　reaction　time　prolongs.　Moreover,　the　possible　scheme　for　the　formation　process　was　discussed　in　detail.　©　2016　Elsevier　B.V.