First observation of J/\psi and \psi(2S) decaying to n K^0_S\bar\Lambda +c.c

The decays of $\jpsi$ and $\psip$ to ${n}{K^0_S}\bar{\Lambda}+c.c.$ are observed and measured for the first time, and the perturbative QCD ``12%'' rule is tested, based on $5.8 \times 10^7$ $\jpsi$ and $1.4 \times 10^7$ $\psip$ events collected with BESII detector at the Beijing Electron-Positron Collider. No obvious enhancement near $n\bar{\Lambda}$ threshold in $\jpsi \to {n}{K^0_S}\bar{\Lambda}+c.c.$ is observed, and the upper limit on the branching ratio of $\jpsi \to {K^0_S} X, X \to n \bar \Lambda$ is determined.