The BESIII experiment has accumulated the world's largest $J/\psi$ sample, and its radiative or hadronic decays offer a unique opportunity to investigate physics in the low-energy region. This report presents the recent highlights in $\eta/\eta'$ decays at BESIII, including evidence of the cusp effect in $\eta'\rightarrow\pi^0\pi^0\eta$, study of the chiral anomaly in $\eta'\rightarrow \pi^+\pi^-\pi^+\pi^-$ and form factor measurements with $\eta/\eta'\rightarrow\gamma e^+e^-$ and $\eta'\rightarrow\pi^+\pi^- l^+l^-$.