This work investigated the surface and biological activity of lactonic and acidic sophorolipid (SL) molecules differing in the acetylation degree of sophorose, carbon chain length and unsaturation degree of the fatty acid moiety. Six different SL molecules were prepared from crude SLs produced by Wickerhamiella domercqiae var. sophorolipid CGMCC 1576. The structures of the selected SL molecules were elucidated by MS and GC/MS. The surface properties of SLs including critical micelle concentration (CMC), minimum surface tension (Min. S.T.) and emulsification capacity to hydrocarbon and vegetable oils were studied, and the results demonstrated that SL molecules with different structures exhibited quite different surface properties. Cytotoxicities of different SL molecules to Chang liver cells determined by the MTT (3-(4,5-dimethythiazol-2-yl)-2,5-diphenyl tetrazolium bromide) method showed the effect of chemical structure of the SLs on their biological activities. Biodegradability of these SL molecules was tested using the river-water die-away method. The differences of surface and biological activity in different SL molecules will be of benefit for the applications of these SLs in specific fields such as the detergent, petroleum, pharmaceutical and environment industries. (C) 2012 Elsevier Inc. All rights reserved.