We report the first direct measurement of decays of the Λ+c baryon involving the neutron. The analysis is performed using 567 pb−1 of e+e− collision data collected at √s=4.599 GeV with the BESIII detector at the BEPCII collider. We observe the decay Λ+c→nK0Sπ+ and measure the absolute branching fraction to be B(Λ+c→nK0Sπ+)=[1.82±0.23(stat)±0.11(syst)]%. A comparison to B[Λ+c→p(¯Kπ)0] provides an important test of isospin symmetry and final state interactions.