  The masses and decay constants of pseudoscalar mesons $ D $, $ D_s $, and $ K
$ are determined in quenched lattice QCD with exact chiral symmetry. For 100
gauge configurations generated with single-plaquette action at $ \beta = 6.1 $
on the $ 20^3 \times 40 $ lattice, we compute point-to-point quark propagators
for 30 quark masses in the range $ 0.03 \le m_q a \le 0.80 $, and measure the
time-correlation functions of pseudoscalar and vector mesons. The inverse
lattice spacing $ a^{-1} $ is determined with the experimental input of $ f_\pi
$, while the strange quark bare mass ($ m_s a = 0.08 $), and the charm quark
bare mass ($ m_c a = 0.80 $) are fixed such that the masses of the
corresponding vector mesons are in good agreement with $ \phi(1020) $ and $
J/\psi(3097) $ respectively. Our results of pseudoscalar-meson decay constant
are: $ f_K = 152(6)(10) $ MeV, $ f_D = 235(8)(14)$ MeV, and $ f_{D_s} =
266(10)(18) $ MeV [hep-ph/0506266]. The latest experimental result of $ f_{D^+}
$ from CLEO [hep-ex/0508057] is in good agreement with our prediction.
