A series of experiments on a mercury spallation target using high-peak-power GeV proton-beam from the Alternating Gradient Synchrotron (AGS) of Brookhaven National Laboratory (BNL) has been performed under an international collaboration among the laboratories in Japan, U.S. and Europe, namely the ASTE (AGS Spallation Target Experiment) collaboration. This paper reviews the current status of the experiments on neutronic performance of the mercury target. © 2014 Atomic Energy Society of Japan.