In this communication, we illustrate a new method to modulate the chemical and mechanical properties of peptide-amphiphile nanofibers. Hydrogels containing a mixture of peptide-amphiphile and phospholipid were prepared and evaluated for their mechanical properties, peptide conformation, and nanostructure. It was found that the storage modulus achieved a maximum at 5 mol % phospholipid and that this coincided with the maximum beta sheet signal as observed by circular dichroism. Throughout the ratios of peptide-amphiphile to phospholipid tested, the storage modulus and peptide secondary structure were closely correlated indicating the coupling between molecular structure and macroscopic properties. The nanostructure of the composite fibers was assessed by vitreous ice cryo-TEM and found to be largely independent of the mixture ratio. These new findings will enhance the versatility of peptide-amphiphiles in nanostructured tissue engineering and drug delivery applications. © 2006 American Chemical Society.