In the sodium dodecyl sulfate (SDS)/n-pentanol (n-C5H11OH)/water (H2O) system, LL is the coexisting region of W/O and O/W or bicontinuous microemulsions. In the LL region, the system separates into two phases (the upper phase and the lower phase) spontaneously. The distribution and Structural behavior of hemoglobin (Hb) between the upper and lower phases in SDS/n-C5H11OH/H2O system were studied by UV-vis and circular dichroism (CD) spectroscopy. The results indicate that different structures of the two phases bring the conformational change of Hb. The addition of Hb results in the redistribution of SIDS between the upper and lower phases. (C) 2008 Published by Elsevier Inc.