The　development　of　a　general　synthetic　approach　for　stable　ultrafine　heterogeneous　nanocatah　sts　has　attracted　extensive　attentions　worldwide.　However,　the　complex　synthetic　process　and　structure　unstability　have　been　recognized　as　the　bottleneck　of　their　investigation　and　practical　application.　Herein,　a　convenient　and　high　selective　platinum　nanocatalyst　was　developed　based　from　crystalline　supramolecular　hybrid　solid　materials.　The　macrocyclic　decamethylcucurbit[5]uril　(Me10CB[5])　and　[PtCl6](2-)　anions　were　firstly　self-assembled　into　cyrstalline　supramolecular　solid　in　the　presence　of　different　alkali　metal　ions　(Li+,　Na+,　K+).　Then,　ultrafine　platinum　(Pt)　nanoparticles　(NPs)　have　been　successfully　synthesized　through　in-situ　reduction　of　cyrstalline　supramolecular　assemblies　under　mild　thermal　treatment　at　H-2　atmosphere.　Uniform　Pt　NPs　(ca.　3.0　nm)　are　produced　and　deposited　on　Me10CB[5]　substrate　to　form　M-Pt@Me10CB[5]　(M=Li+,　Na+,　K+)　composite　materials.　The　obtained　Pt　NPs　are　characterized　extensively　by　a　range　of　physical　measurements　including　X-ray　powder　diffractions　(PXRD),　thenuogravimetric　analyses　(TGA),　inductively　coupled　plasma　emission　spectrometer　(ICP),　X-ray　photoelectron　spectroscopy　(XPS)　and　transmission　electron　microscope　(TEM).　The　morphology　and　size　of　Pt　NPs　can　be　easily　tuned　through　changing　the　original　supramolecular　structures.　The　different　interaction　between　[PtCl6](2-)　and　Me10CB[5]　capsulates　affects　the　morphology　and　size　of　Pt　NPs　greatly.　Such　differences　in　geometric　structures　of　Pt　NPs　have　a　significant　impact　on　their　catalytic　performance.　Moreover,　the　unique　confinement　effect　provided　by　the　supramolecular　assembly　as　well　as　the　special　steric　effect　offered　by　macrocyclic　Me10CB[5]　suppresses　the　growth　of　Pt　NPs　during　the　reduction　process.　In　addition,　the　atomic　level　uniform　dispersion　of　Pt　ions　in　ordered　crystalline　structure　of　the　supramolecular　assembly　assures　the　uniform　distribution　of　the　final　Pt　NPs　on　the　intact　Me10CB[5],　which　acts　as　both　a　stabilizer　and　support.　The　Pt　NPs　obtained　from　Na+　and　K+　constructed　supramolecular　assemblies　exhibit　high　activity　and　chemoselectivity　in　catalytic　hydrogenation　of　substituted　nitrobenzenes　to　corresponding　anilines　under　mild　conditions.　Meanwhile,　the　final　Pt　NPs　also　show　an　excellent　stability　in　recycle　test　without　dramatic　loss　of　activity.　This　work　demonstrates　a　novel,　high-performance　catalyst　for　the　chemoselective　hydrogenation　reaction,　and　opens　up　a　new　approach　for　the　preparation　of　nanocatalysts,　which　can　be　used　in　many　other　important　fields,　such　as　electrochemistry,　energy　science　and　environmental　protection.