Ordered arrays of FePt nanoparticles were prepared using a diblock polymer micellar method combined with plasma treatment. Rutherford backscattering spectroscopy analyses reveal that the molar ratios of Fe to Pt in metal-salt-loaded micelles deviate from those when metal precursors are added, and that the plasma treatment processes have little influence upon the compositions of the resulting FePt nanoparticles. The results from Fourier transform infrared spectroscopy show that the maximum loadings of FeCl(3) and H(2)PtCl(6) inside poly(styrene)-poly(4-vinylpyridine) micelles are different. The composition deviation of FePt nanoparticles is attributed to the fact that one FeCl(3) molecule coordinates with a single 4-vinylpyridine (4VP) unit, while two neighboring and uncomplexed 4VP units are required for one H(2)PtCl(6) molecule. Additionally, we demonstrate that the center-to-center distances of the neighboring FePt nanoparticles can also be tuned by varying the drawing velocity.