We have demonstrated that poly(2-aminothiophenol)-stablized gold nanoparticles with proper gold size and polymer thickness are active catalysts for Suzuki-Miyaura Cross-coupling reaction of aryl halides with arylboronic acids in water and air for the first time. High yields can be obtained with aryl halides or arylboronic acids bearing a variety of substituents. This new finding will undoubtedly broaden the application of gold nanoparticles in organic catalytic reactions.