  In the Euclidean path integral approach, we calculate the actions and the
entropies for the Reissner-Nordstr\"om-de Sitter solutions. When the
temperatures of black hole and cosmological horizons are equal, the entropy is
the sum of one-quarter areas of black hole and cosmological horizons; when the
inner and outer black hole horizons coincide, the entropy is only one-quarter
area of cosmological horizon; and the entropy vanishes when the two black hole
horizons and cosmological horizon coincide. We also calculate the Euler numbers
of the corresponding Euclidean manifolds, and discuss the relationship between
the entropy of instanton and the Euler number.
