  Measurements from the RHIC experiments show strong suppression of high-pT
hadrons in central Au+Au collisions. The PHENIX experiment has observed strong
suppression of $\pi^0$ and charged hadron yields in central Au+Au collisions
for pT > 5 GeV/c regardless of pT and particle species. The observed
suppression is interpreted in terms of energy loss of quarks in a high-density
medium.
  The PHENIX Year-4 Au+Au measurements have extended the pT reach of the
$\pi^0$ spectra to 20 GeV/c. And the PHENIX Year-5 Cu+Cu measurements performed
for the study of particle production in a lighter system and they can provide
the system-size dependence of the suppression. The suppression patterns of
$\pi^0$/$\eta$ at high pT are presented for each collision system
(Au+Au/Cu+Cu).
