A　simple,　rapid,　field-portable　colorimetric　method　for　the　detection　of　melamine　based　on　melamine-induced　color　change　of　label-free　gold　nanoparticles　(Au　NPs)　was　developed　in　this　study.　Melamine　can　induced　the　aggregation　of　Au　NPs　and　results　in　the　color　change　from　wine-red　to　purple,　which　provided　a　platform　for　rapid　and　field-portable　colorimetric　detection　of　melamine.　The　proposed　method　can　be　used　to　detect　melamine　in　liquid　milk　and　infant　formula　with　a　detection　limit　of　1.0　and　4.2　ppm,　respectively,　within　30　min　by　naked　eyes　observation　without　the　aid　of　any　advanced　instrument　and　the　need　of　any　complex　pretreatment,　and　detect　as　low　as　0.15　ppm　of　melamine　in　liquid　milk　and　2.5　ppm　of　melamine　in　infant　formula　with　UV-vis-spectroscopy.　The　proposed　method　is　promising　for　on-site　screening　of　melamine　adulterant　in　milk　products.　(C)　2010　Elsevier　BM.　All　rights　reserved.