  We have searched for the decay KS->gg in a sample of 2x10^9 phi->KS KL decays
collected at DAPHNE with an integrated luminosity of 1.9 fb^{-1}. KS are tagged
by the KL interaction in the calorimeter. Two prompt photons must also be
detected. Kinematic constraints reduce the initial 6x10^5 events to 2740
candidates, from which a signal of 711\pm 35 events is extracted. By
normalizing to the KS->2pi^0 decays counted in the same sample, we measure
BR(KS->gg)= (2.26\pm0.12_{stat}\pm0.06_{syst})x10^{-6}, in agreement with
O(p^4) Chiral Perturbation Theory predictions.
