Based on the swelling action of organic solvents on hollow-fiber membranes, a new technique of solvent-swelling and dry-shaping for preparing coiled hollow fibers from straight hollow fibers was introduced. The mass transfer performance of these coiled fibers was tested with 30% TBP (in kerosene)-phenol-water as a working system in a membrane extraction process, and compared with the results obtained from the straight fibers. After long time test, it was proved that the coiled fibers were stable when they contacted with the organic solvent in the membrane extraction process. As to the mass transfer performance, it was found that the presence of vortices in the coiled fibers provided better mass transfer performance than the straight fibers. The improvement factor was in the range of 2-4. With an increase of the phase velocity inside the tube, the mass transfer coefficient and energy input in the coiled fibers grew up much more quickly than that in the straight fibers. An empirical correlation for predicting the mass transfer coefficients and an equation for pressure drop in the coiled fibers were suggested. (C) 2003 Elsevier Science B.V. All rights reserved.