This　paper　designs　a　novel　path　planner　for　unmanned　aerial　vehicle　(UAV)　in　the　three-dimensional　terrain　environment　using　the　fruit　fly　optimization　algorithm　(FOA).　The　UAV　path　planning　problem　is　formulated　as　an　optimization　problem,　using　the　B-Spline　curve　to　represent　flight　paths.　The　cost　function　adopting　herein　to　evaluate　the　flight　path　contains　multiple　optimization　indexes　and　performance　constraints.　Detailed　process　of　the　FOA-based　path　planner　is　proposed　to　find　the　optimal　path　with　the　minimum　cost　function　value.　Numerical　simulations　are　carried　out　and　the　results　show　that　FOA　is　the　powerful　optimization　technique　in　solving　UAV　path　planning　problem.