Concentration monitoring is essential for quality control of crystallizations. This work establishes the technical feasibility of Ultraviolet (UV) fiber spectroscopy for on-line concentration measurement of anti-solvent crystallization of beta-artemether, where ethanol was selected as solvent and water was used as anti-solvent. The orthogonal signal correction (OSC) algorithm was selected to preprocess the UV spectra, and the results showed that the wavelength shift of UV maximum absorbance of beta-artemether in ethanol + water solvent mixtures can be effectively eliminated by OSC algorithm. Then models for prediction of beta-artemether concentration based on Lambert-Beer law were developed, and the models were verified by comparison between the training set and the validation set, as well as its directly application to the anti-solvent crystallization process of beta-artemether. The results show that the model is suitable for on-line concentration measurement of anti-solvent crystallization of beta-artemether, with reasonable accuracy and precision. (C) 2010 Elsevier B.V. All rights reserved.