Rare decays are an ideal laboratory to test the predictions of the Standard Model. Moreover, charm and charmonium rare decays have branching ratios so small that any observation would immediately lead to a New Physics scenario. The BESIII experiment can study with unprecedented precision the charmonium weak decays, owing to the world's largest charmonium dataset. Moreover, it can provide complementary information with respect to the B-factories to the Long Distance (LD) process in charmed meson weak decays studies. In this presentation, we report some of the most recent searches performed by the BESIII collaboration.