  Based on the slave-boson theory of the two-dimensional $t-t'-J$ model, we
calculate the superconducting condensation energy for optimally doped and
overdoped high $T_{c}$ cuprates at finite temperatures using a renormalized
random phase approximation. The contributions come from the mean-field part and
the antiferromagnetic spin fluctuations. In the presence of neutron resonance
peak at $(\pi,\pi)$, the latter is shown to have similar temperature and doping
dependences as the difference in antiferromagnetic (AF) exchange energy between
the normal and the superconducting state. This difference has been proposed to
be related to the superconducting condensation energy by Scalapino and White.
The total condensation energy, however, is about 1/2 smaller than the proposed
AF exchange energy difference and shows a more rapid decrease as the
temperature rises. The doping dependence of the condensation energy is found to
be consistent with experiments. In particular, near zero temperature, our
result shows a good quantitative agreement with experiments.
