A　methylene　blue-based　near-infrared　fluorescent　probe　was　designed　for　the　selective　determination　of　hypochlorite　(ClO-),　over　other　reactive　oxygen　species　or　interfering　agents.　Acetylated　methylene　blue　was　synthesized　by　introducing　the　acetyl　group　into　the　methylene　blue　framework,　which　can　specifically　recognize　exogenous　and　endogenous　ClO-.　The　acetylated　methylene　blue　fluorescent　probe　was　characterized　by　H-1　NMR,　C-13　NMR　and　HRMS.　The　response　process　and　possible　mechanism　were　studied　using　products　of　the　probe.　The　emission　response　of　the　probe　to　ClO-　presented　good　linear　relationship　in　the　0-60　M　concentration　range,　with　the　detection　limit　of　0.1　M　(measured　at　660　nm　and　690　nm).　The　absorption　and　emission　wavelengths　of　acetylated　methylene　blue　are　both　in　the　near-infrared　region;　in　addition,　the　probe　itself　and　the　degradation　products　were　well-dissolved　in　water　and　have　almost　no　toxicity.　The　probe　was　used　for　intracellular　ClO-　imaging　and　showed　a　large　fluorescence　enhancement　(about　200-fold　increase).