AdS3 black hole entropy and the spectral flow on the horizon

. We consider the entropy problem of AdS(3) black holes by using the conformal field theory at the horizon. We observe that the supersymmetry is enhanced at the horizon of a massless AdS(3) black hole. This allows us to determine the vacuum of the modular invariant conformal field theory to be the Neveu-Schwarz(NS)-ground state (which corresponds to AdS(3) spacetime). This is smoothly related to the Ramond(R)-ground state (corresponding to a massless black hole) by a spectral flow, which can be understood as a superconformal transformation.