  Discussed is how non-perturbative properties of quark gluon plasma, recently
discovered in RHIC experiment, can be related to the change of properties of
scalar and pseudoscalar glueballs. We set up a model with the Cornwall-Soni's
glueball-gluon interaction, which shows that the pseudoscalar glueball becomes
massless above the critical temperature of deconfinement phase transition. This
change of properties gives rise to the change of sign of the gluon condensate
at $T > T_c$. We discuss the other physical consequences resulting from the
drastic change of the pseudoscalar glueball mass above the critical
temperature.
