Gold　nanoparticles　(AuNPs)　have　been　frequently　utilized　for　the　construction　of　diverse　colorimetric　biosensors.　Normally,　AuNPs　with　sharp　edges　could　have　better　sensitivity.　However,　the　poor　monodipersity　of　AuNPs　with　sharp　edges　seriously　confines　their　utility　for　colorimetric　biosensing.　Herein,　we　demonstrate　the　utility　of　highly　uniform　gold　nanobipyramids　(Au　NBPs)　for　ultrasensitive　colorimetric　detection　of　H5N1　virus.　The　proposed　method　is　based　on　the　fact　that　alkaline　phosphatase　(ALP)　could　catalyze　the　decomposition　of　4-aminophenyl　phosphate　(4-APP)　to　generate　4-aminophenol　(4-AP),　which　would　then　reduce　silver　nitrate　to　metal　silver　and　then　deposited　on　Au　NBPs.　The　metal　silver　shell　coated　on　the　Au　NBPs　changed　the　refractive　index　of　gold　and　thus　resulted　in　a　blue　shift　of　longitudinal　localized　surface　plasmon　resonance　(LSPR)　and　accompanied　a　vivid　color　change.　This　method　exhibited　a　higher　sensitivity　than　that　of　other　Au　NPs　such　as　gold　nanorods　due　to　the　high-index-faceted　on　the　tips　of　the　Au　NBPs.　This　method　was　used　to　detect　the　activity　of　ALP.　It　exhibited　a　linear　range　of　0.1-5　mU/mL　with　a　limit　of　detection　(LOD)　of　0.086　mU/mL.　Finally,　the　proposed　method　was　used　in　immunoassay　to　detect　H5N1　virus.　The　results　showed　that　the　corresponding　linear　range　for　the　detection　of　H5N1　virus　antigen　was　0.001-2.5　ng/mL,　and　the　LOD　was　determined　to　be　1　pg/mL,　which　is　more　sensitive　than　those　in　most　of　the　colorimetric　biosensors　reported　previously.　©　2016　American　Chemical　Society.