New flavor symmetry and nonleptonic decays ofDandBmesons

New flavor symmetry of heavy quarks is studied in $D$ meson and $B$ meson decays. Form factors of the $\overline{B}\to K, K^{*}$ transition are obtained from observed form factors in semileptonic decays of the $D$ meson owing to flavor symmetry. Branching ratios of nonleptonic decays $\overline{B}\to K\psi \mathrm{and} K^{*}\psi$ are predicted, using the $\frac{1}{N_c}$ expansion of the weak hadronic matrix element. Our results agree nicely with experimental branching ratios.