  Based on $e^+e^-$ collision data corresponding to an integrated luminosity of
4.5 $fb^{-1}$ collected at the center-of-mass energies between 4.600 and 4.699
GeV with the BESIII detector at BEPCII, the absolute branching fraction of the
inclusive decay $\Lambda^{+}_{c}\to n + X$, where $X$ refers to any possible
final state particles, is measured. The absolute branching fraction is
determined to be $\mathcal{B}(\Lambda^{+}_{c}\to n + X) = (32.4 \pm 0.7 \pm
1.5)\% $, where the first uncertainty is statistical and the second systematic.
Assuming $CP$ symmetry, the measurement indicates that about one-fourth of
$\Lambda^{+}_{c}$ ($\bar{\Lambda}_{c}^-$) decay modes with a neutron (an
anti-neutron) in the final state have not been observed.
