The micelle-to-vesicle transition of AOT in aqueous solution was well detected by fluorescence technique using Nile red (NR) as the probe. The results showed that the first turning points on I-a-C and I-a/I-b-C curves indicated the critical micelle concentration (cmc) of AOT, while the maximum in I-a/I-b-C curve well responded to vesicle formation. This is due to different locations of the probe in micelle and vesicle. In comparison with p-N,N-dimethylaminobenzonitrile (DMABN), the information about the molecular structure of the probe required to detect effectively the micelle-to-vesicle transition was obtained. (C) 2008 Elsevier B. V. All rights reserved.