The　mononuclear　phagocyte　system　(MPS)　with　key　roles　in　recognition　and　clearance　of　foreign　particles,　is　a　major　constraint　to　nanoparticle-based　delivery　systems.　The　desire　to　improve　the　delivery　efficiency　has　prompted　the　search　for　stealthy　long-circulating　nanoplatforms.　Herein,　we　design　an　antiphagocytic　delivery　system　with　＇active＇　stealth　behavior　for　cancer　theranostics　combining　efficient　MRI　and　enhanced　drug　delivery.　We　modify　self-peptide,　a　synthetic　peptide　for　active　immunomodulation,　to　biodegradable　poly(lactide-glycolide)-poly(ethylene　glycol)　(PLGA-PEG),　then　utilize　the　self-assembly　properties　of　PLGA-PEG　to　form　nanomicelles　that　encapsulating　iron　oxide　(IO)　nanoparticles　and　anticancer　drug　paclitaxel　(PTX).　Through　the　interaction　of　self-peptide　with　the　receptor　SIRPα,　which　is　expressed　on　phagocytes,　the　as-prepared　nanomicelles　can　disguise　as　＇self＇　to　avoid　being　recognized　as　foreign　particles　by　MPS,　leading　to　improved　blood　circulation　time　and　delivery　efficiency.　Compared　to　the　＇passive＇　stealth　effect　generating　by　PEG　or　zwitterionic　polymers　that　only　passively　delay　the　physisorption　of　serum　proteins　to　nanocarriers,　the　＇active　self＇　nanomicelles　can　more　efficiently　inhibit　the　MPS-mediated　immune　clearance　and　reduce　＇accelerated　blood　clearance＇　phenomenon.　Furthermore,　this　one-step　clustering　of　IO　nanoparticles　and　loading　of　PTX　endow　the　resulted　magneto-nanomicelles　with　enhanced　T2　MRI　contrast　performance　and　antitumor　effect.　We　believe　that　this　study　provides　a　novel　approach　in　designing　of　efficient　stealth　antiphagocytic　delivery　systems　that　resisting　the　MPS-mediated　clearance　for　cancer　theranostics.　©　2017　American　Chemical　Society.