The dependency of static stability N2 of the Jovian atmospheres on the abundances of condensible elements is considered by calculating the moist adiabatic profiles. An optimal minimization method of the Gibbs free energy is utilized to obtain equilibrium compositions in order to cover a variety of basic elements. It is shown that CH4 is one of the dominant contributors to producing a stable layer in the Uranian atmosphere. On Jupiter, R. K. Achterberg and A. P. Ingersoll (1989) have shown that, at low water abundances, N2 is proportional to the H2O abundance. In the present study, we show that this relationship does not hold when the H2O abundance is larger than approximately 5 ¿ solar. A rough estimation of wave speed indicates that the abundance of 10 ¿ solar is marginal to explain the SL9-induced wave speed as that of an internal gravity wave.