羟磷灰石（英语：hydroxyapatite），又称氢氧基磷灰石，是一种天然的磷灰石矿物，其分子式为Ca₅(PO₄)₃(OH)，不过常写成Ca₁₀(PO₄)₆(OH)₂以表示由二个分子组成的晶体结构。羟磷灰石是磷灰石中含氢氧根的纯正端元（endmember）。OH离子可以被氟离子、氯离子或碳酸根离子取代，形成氟磷灰石（fluorapatite）或氯磷灰石（chlorapatite）。羟磷灰石的晶系为六方晶系，比重为3.08，摩氏硬度为5。纯的羟磷灰石粉末是白色，但天然的羟磷灰石会夹杂着棕色、黄色或绿色。也可以用人工的方式合成，应用于骨组织修复。

Hydroxylapatite, also called hydroxyapatite (HA), is a naturally occurring mineral form of calcium apatite with the formula Ca₅(PO₄)₃(OH), but is usually written Ca₁₀(PO₄)₆(OH)₂ to denote that the crystal unit cell comprises two entities. Hydroxylapatite is the hydroxyl endmember of the complex apatite group. The OH ion can be replaced by fluoride, chloride or carbonate, producing fluorapatite or chlorapatite. It crystallizes in the hexagonal crystal system. Pure hydroxylapatite powder is white. Naturally occurring apatites can, however, also have brown, yellow, or green colorations, comparable to the discolorations of dental fluorosis.