Protamine, a kind of cationic protein extracted from sperm nuclei, was employed for the first time in vitro to induce the formation of a titania/protamine nanoparticle composite from a water-stable titanium precursor, titanium(IV) bis(ammonium lactato) dihydroxide (Ti-BALDH). The resulting titania/protamine nanoparticle composite was extensively characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The titania/protamine nanoparticle composite was of amorphous structure, and exhibited a different morphology from those prepared by an alkali-catalyzed approach. The catalyzing and templating function of protamine involved in the synthesis of the nanoparticle composite is discussed, and a mechanism tentatively proposed. In addition, the effects of pH and temperature on the amount and size of as-prepared titania/protamine nanoparticle composite were systematically investigated.