At present the world's largest sample of 1.3 billion J/psi events was accumulated at the BESIII detector, which provides a unique opportunity to investigate the eta/eta' decays via J/psi radiative or hadronic decays. The eta and eta' hadronic decays are sensitive tools for investigations of pi-pi and eta-pi interactions, symmetry breaking, and serve as a test of Chiral Perturbation Theory. In recent years considerable results on eta/eta' decays were achieved at BESIII experiment. In this talk we present the significant progresses focusing on amplitude analyses of Dalitz decays (e.g. eta'->3 pi PRL 118, 012001 (2017) ), observation new decay modes and search for rare/forbidden decays (e.g. eta'->gamma gamma pi0, arXiv: 1612.05721).