By analyzing 2.93 fb −1 of e + e − collision data taken at the center-of-mass energy of 3.773 GeV with the BESIII detector, the branching fractions of the inclusive decays D + → K 0 S X and D 0 → K 0 S X are measured to be (32.78 ± 0.13 ± 0.27)% and (20.54 ± 0.12 ± 0.18)%, respectively, where the first uncertainties are statistical and the second are systematic. These results are consistent with the world averages of previous measurements, but with improved precision.