We show a Poisson formula for bounded harmonic functions Phi on the Sierpin
ski gasket Y. We construct a boundary (<(Sigma)over tilde>, <(nu)over tilde
>, S), a measurable action of a semigroup W on <(Sigma)over tilde> and a ma
p Gamma: W --> Y, such that for every bounded harmonic function Phi on Y Ph
i(Gamma (w)) = integral(<(Sigma)over tilde>) Psi(w xi)<(nu)over tilde>(d xi
), where Psi : <(Sigma)over tilde> --> R is some bounded measurable functio
n.