Marine mussels utilize multiple bidentate complexes formed by Fe(iii) and DOPA in a mussel adhesive protein (fp-1) to reinforce tough and elastic byssal fibers as a specialized underwater adhesive aid. In this study, mussel-inspired electrospun nanofibers were fabricated using a recombinant mussel adhesive protein (rfp-1), Fe(iii)-DOPA complexes, and polycaprolactone. The mechanical properties of the fabricated nanofibers were reinforced by the Fe(iii)-DOPA complex found in fp-1, which is a key component of the naturally occurring high-performance mussel fiber coating. Experimental results show that the stoichiometry of Fe(iii)-DOPA complexes in the nanofibers could be controlled by buffer pH conditions and the stiffness of the nanofiber mat increased linearly with the concentration of the Fe(iii)-DOPA complexes, as monitored by resonance Raman spectroscopy. This suggests the potential of Fe(iii)-DOPA complexation as an effective strategy for modulating the mechanical properties of nanofibrous biomedical materials by using pH variations.