Bovine serum albumin (BSA) nonspecifically binds to well-dispersed multiwalled carbon nanotubes (MWCNTs), forming a stable bioconjugate. After accounting for the inner filter effect, we found the fluorescence intensity of BSA was quenched by MWCNTs in static mode, which was authenticated by lifetime measurements and Stern-Volmer calculations. The thermodynamic parameters Delta G degrees, Delta S degrees, and Delta H degrees were -9.67 x 10(3) + 2.48 x 10(3) In lambda J.mol(-1), 41.0-0.828 In lambda J.mol(-1)center dot K-1 and 7.30 x 10(3) + 2.23 x 10(3) In lambda J.mol(-1) (lambda < 1 x 10(-4)), respectively, which shows a spontaneous and electrostatic interaction. Scatchard analysis and UV-visible results provide statistical data concerning changes in the microenvironment of amide moieties in response to different doses of MWCNTs, revealing different behavior of the BSA molecules. The absorption spectra also show that the tertiary structure of the protein was partially destroyed. The content of secondary structure elements of BSA was changed by the tubes. This work elucidates the interaction mechanism of BSA and MWCNTs from a spectroscopic angle.