This paper investigates the effect of CFO gender on corporate tax aggressiveness. Focusing on firms that experience a male-to-female CFO transition, the paper compares those firms' degree of tax aggressiveness during the pre-and posttransition periods. Using the probability of tax sheltering, the predicted unrecognized tax benefits, and the discretionary permanent book-tax differences to measure tax aggressiveness, we find that female CFOs are associated with less tax aggressiveness as compared to their male counterparts. The main findings are supported by additional tests based on propensity score matching, difference-in-difference tests, and tests with a female-to-male CFO transition sample. Overall, our study establishes CFO gender as an important determinant of tax aggressiveness.