Searches for very rare decays to purely leptonic final states at LHCb

Rare leptonic decays of the B 0 ( s ) mesons are sensitive probes of New Physics. The LHCb exper- iment is well suited for these analyses due to its large acceptance and trigger efficiency, as well as its excellent invariant mass resolution and lepton identification capabilities. The latest LHCb results on the searches of B 0 ( s ) ! m + m rare decay and B 0 ( s ) ! e m lepton flavour violating decay are presented.