  In the Standard Model, charged lepton flavor violation (CLFV) is heavily
suppressed by tiny neutrino mass, while many theoretical models can enhance
CLFV effects up to a detectable level. The observation of any CLFV process
would be a clear signal of new physics beyond SM. BESIII experiment collected
10 billion $J/\psi$ data and searched for CLFV processes $J/\psi\to e\tau$ and
$e\mu$. The upper limits at the 90% confidence level are determined to be
$\mathcal{B}(J/\psi\to e\tau)<7.5\times 10^{-8}$ and $\mathcal{B}(J/\psi\to
e\mu)<4.5\times 10^{-9}$, respectively. Improving the previously experimental
limits by two orders of magnitudes, the results are the most stringent CLFV
searches in the heavy quarkonium system.
