Doping　Mn　(II)　ions　into　iron　oxide　(IO)　as　manganese　ferrite　(MnIO)　has　been　proved　to　be　an　effective　strategy　to　improve　T-1　relaxivity　of　IO　nanoparticle　in　recent　years;　however,　the　high　T-2　relaxivity　of　MnIO　nanoparticle　hampers　its　T-1　contrast　efficiency　and　remains　a　hurdle　when　developing　contrast　agent　for　early　and　accurate　diagnosis.　Herein,　we　engineered　the　interfacial　structure　of　IO　nanoparticle　coated　with　manganese　ferrite　shell　(IO@MnIO)　with　tunable　thicknesses.　The　Mn-doped　shell　signifi-cantly　improve　the　T-1　contrast　of　IO　nanoparticle,　especially　with　the　thickness　of-0.8　nm.　Compared　to　pristine　IO　nanoparticle,　IO@MnIO　nanoparticle　with　thickness　of-0.8　nm　exhibits　nearly　2　times　higher　T-1　relaxivity　of　9.1　mM(-1)s(-1)　at　3　T　magnetic　field.　Moreover,　exclusive　engineering　the　interfacial　structure　significantly　lower　the　T-2　enhancing　effect　caused　by　doped　Mn　(II)　ions,　which　further　limits　the　impairing　of　increased　T-2　relaxivity　to　T-1　contrast　imaging.　IO@MnIO　nanoparticles　with　different　shell　thicknesses　reveal　comparable　T-1　relaxation　rates　but　obvious　lower　T-2　relaxivities　and　r(2)/r(1)　ratios　to　MnIO　nanoparticles　with　similar　sizes.　The　desirable　T-1　contrast　endows　IO@MnIO　nanoparticle　to　pro-vide　sufficient　signal　difference　between　normal　and　tumor　tissue　in　vivo.　This　work　provides　a　detailed　instance　of　interfacial　engineering　to　improve　IO-based　T-1　contrast　and　a　new　guidance　for　designing　effective　high-performance　T-1　contrast　agent　for　early　cancer　diagnosis.　(C)　2022　Elsevier　Inc.　All　rights　reserved.