beta-Xylosidase, an enzyme produced by Penicillium janthinellum fungus, was prepurified by fractionated precipitation with ethanol and extracted by reversed micelles of N-benzyl-N-dodecyl-N-bis(2-hydroxyethyl) ammonium chloride (BDBAC) cationic surfactant. A 2(5-1) fractional factorial design was employed to evaluate the influence of the following factors on the enzyme extraction: pH (A), conductivity (B), surfactant concentration (C), cosolvent concentration (D) and temperature (E). A statistical analysis of the results revealed that, of the five variables studied, pH, surfactant concentration, and temperature had significant main effects (p < 0.05) on the recovery of beta-xylosidase (Y). However, the interactions between pH and temperature, conductivity and cosolvent concentration, conductivity and temperature, BDBAC concentration and temperature also had significant influences. A first-order model (R-2 = 0.98) expressed by the equation Y = 7.73 - 5.55A - 0.67B + 3.49C - 0.41D + 5.26E + 2.05AB - 3.26AC + 0.96AD - 7.07AE - 3.93BD - 2.19BE + 0.99CD + 0.78CE was proposed to represent the enzyme recovery as a function of the effects that were really significant. This model predicts a recovery value of about 40%, which is similar to that obtained experimentally (39.5%).