Search for the weak decay *

Using $(448.1 \pm 2.9) \times 10^{6}$ $\psi(3686)$ events collected with the BESIII detector, we perform first search for weak baryonic decay $\psi(3686) \to \Lambda_c^{+} \bar{\Sigma}^- +c.c.$. The analysis procedure is optimized using a blinded method. No significant signal observed, and upper limit on branching fraction ($\mathcal B$) of +c.c.$ set to be $1.4\times 10^{-5}$ at 90\% confidence level.