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Bimetallic CuPt nanocrystals with size ranging from 3 to 30 nm were synthesized in the presence of either hexadecylamine or poly(vinylpyrrolidone) as a capping agent. Different growth stages of CuPt nanoparticles prepared with hexadecylamine have been investigated and a non-classic mechanism governing the formation of the metal alloy was revealed. It was found that the precursor molecules aggregate into amorphous spheres at a very early stage, followed by surface multiple nucleation, formation and combination of crystalline islands to produce a core-shell structure with surface-to-core extension of the crystallization to achieve single crystals. CuPt nanocrystals synthesized with poly (vinylpyrrolidone) grew via the classic route. Dealloying treatment was applied on these CuPt nanoalloys to selectively remove Cu. Large particles (?30 nm) with Cu-rich cores exhibited hollow structures after dealloying while 3 nm particles remained solid, demonstrating that particle size and composition have a great influence on the final morphology of dealloyed particles.