Blends of Nylon 66(Ny66) and polyethylene naphthalate (PEN) with 30, 50, 70 wt % Ny66, and one blend with 50% Ny66 and 3% compatibilizer, prepared by extrusion and injection molding, were investigated using C-13 and H-1 nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS),and scanning electron microscopy (SEM). A new band in the FTIR spectra of blends, at 1324-1329 cm(-1) is interpreted as arising from partial reaction of Ny66 and PEN occurring during melt processing. However, NMR spectra show no evidence of interchange reaction between Ny66 and PEN. SEM indicates that the phase inversion point is close to equal proportions by weight of the two homopolymers.