In this talk we present the latest results on radiative and rare/forbidden decays for D and D_s mesons from the BESIII experiment based on 2.92 fb$^{-ˆ’1}$ and 3.19 fb$^{-1}$ data samples taken at the center-of-mass energies 3.773 and 4.178 GeV, respectively. With the 4.178 GeV data, searches for the rare decay $D^+_S\to p\bar{p}e^+\nu_e$ and rare radiative leptonic decay $D_S^+\to\gamma e^+\nu_e$ are performed for the first time, both with negative results; branching fraction (BF) upper limits (ULs) are at 90\% confidence levels (CL) will be reported. With the 3.773 GeV dataset, we search for the rare decays $D\to h(h^\prime)e^+e^-$ with a double tag method, where $h(^\prime)$ are different hadrons. No significant excesses over the expected backgrounds are observed. For $D^+$ decays, the searches are performed for the first time, while for $D^0$ decays, the ULs are in general improved by an order of magnitude compared to previous measurements. All of the BF ULs are in the $10^{-5~-6}$ range and above SM predictions that include both long- and short-distance contributions. Also, we searched for signs of a Majorana neutrino in the lepton number violating (LNV) decays $D\to K\pi e^+e^+$. No significant signal is observed. Effects of Majorana neutrinos with different mass assumptions that range from 0.25 to 1.0 GeV are searched for in the decays $D^0\to K^-e^+\nu_N(\pi^-e^+)$ and $D^+\to K^0_Se^+\nu_N(\pi^-e^+)$. Constraints on the mixing-matrix element $|V_{eN}|^2$ are also evaluated.