Abstract The effect of alkyl sulfates of various chain lengths on immunoglobulin fragment Fc(t) was studied. Circular dichroism measurements indicated that the non-helical polypeptide chains of Fc(t) were ordered by anionic detergents to a certain degree. Resolution of the ellipticity curves into Gaussian peaks showed that the detergents incited the formation of negative bands centered at 206 and at 222 nm and a positive band at 190–192 nm. This partial transition to α-helical structure was enhanced by increasing amount of detergents until the critical micelle concentrations of the detergents were reached, when no further change was observed with additional detergents. The effect of ionic strength seemed to be on the critical micelle concentration. These conformational changes were also influenced by pH and the hydrophobic chain length of the detergents. In acid solution, anionic detergents appeared to both promote α-helix formation and reduce the amount of disordered structure present in Fc(t). The order of effectiveness of the detergents as helix-forming agents was tetradecyl > dodecyl > decyl > octyl sodium sulfate, indicating the importance of hydrophobic bonding in Fc(t). In near ultraviolet zone, the circular dichroic bands were weakened by the detergents, although the Cotton effects were not completely eliminated.