Herein,　a　novel　palladium-doped　graphitic　carbon　nitride　nanosheet　(g-C3N4-PdNPs)　is　reported.　The　prepared　g-C3N4-PdNPs　has　a　6.7　and　14.0　times　higher　peroxidase-like　activity　in　comparison　with　pure　Pd　nanoparticles　(PdNPs)　and　graphitic　carbon　nitride　(g-C3N4)　nanosheets　respectively,　and　can　be　stably　stored　for　3　months.　The　high　peroxidase-like　activity　make　g-C3N4-PdNPs　effectively　catalyze　H2O2-mediation　oxidization　of　3,3,5,5′-tetramethylbenzidine　to　generate　a　color　change　from　colorless　to　blue　under　lower　concentration　level　and　shorter　time.　The　g-C3N4-PdNPs　can　be　used　as　peroxidase　mimetic　to　develop　sensitive　and　specific　colorimetric　method　for　the　rapid　detection　of　glucose　in　the　serum,　and　to　fabricate　a　simple　and　cheap　portable　test　kit　for　instrument-free　visual　detection　of　glucose　in　serum.　The　portable　test　kit　possesses　obvious　advantages　such　as　low-cost,　short　detection　time,　tiny　sample　consumption,　excellent　specificity,　and　higher　visual　sensitivity.　The　visual　detection　limit　of　portable　test　kit　is　lower　than　the　glucose　concentration　in　the　serum　of　a　diabetic.　Using　portable　test　kit,　the　glucose　in　serum　can　be　visually　detected　by　bare　eye　observation　within　30　min　with　only　30　µL　serum　consumption.　The　success　of　this　study　provided　a　potential　approach　for　low-cost　and　instrument-free　＇see＇　diabetes　in　clinical　early　diagnosis.　©　2017　WILEY-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim