Objective: The interaction between six micromolecules of cholic acids (CAs) and bovine serum albumin (BSA) was investigated by fluorescence spectroscopy (FS) combined with FT-ATR-IR and the six CAs were cholic acid (CA)

deoxycholic acid (DCA)

hyodeoxycholic acid (HDCA)

chenodeoxych-olic acid (CDCA)

taurochenodeoxycholic acid (TCDCA)

ursodesoxycholic acid (UDCA) respectively. Method: According to the dynamic quenching rate constants Kq of Stern-Volmer equation

we could infer the fluorescence quenching mechanism of BSA under the simulated physiological conditions (at pH 7.40 and ionic strength=0.15 mol·L-1). The binding constants KLB

binding site numbers n

every type of conjugation effort according to the stemvolmer equation

Lineweaver-Burk equation

langmuir equation; thermodynamic parameters. Synchronous fluorescence technique and FT-ATR-IR. Result: CAs could insert into the BSA molecule initiatively with the ratio of 0.5:1

namely two protein molecules binding with one of cholic acid compounds molecular to become ground-state complex substances which resulted into intrinsic fluorescen-ce quenching. And with the increasing concentration of CAs

their combination tended to saturation. But the combination of CAs and BSA were relatively weaker as the binding constant KLB is lower than that of inter-acttions of other drugs with protein. The interaction force was mainly hydrogen bonds or Vander Walls force between CAs and BSA

with the possible force of electrostatic interaction. The influence on the framework of BSA was not obvious. Conclusion: There is certain binding interaction between CAs and BAS which provides the conditions for storage and transport of protein in the body. At the same time

the interactional mechanism was clarified

and the theoretical basis was provided for the further study of the inner mechanism and biological effect in organism of CAs and the proteins.