Let H be the Stark operator in R-3 and let V = V (x) be a non-negative potential which decays at infinity as | x|(- l) for a sufficiently large l > 0. The spectral shift function for the pair of operators H + tV, H is studied in the asymptotic regime t --> infinity. The leading term of the asymptotics is obtained; the result is in agreement with the phase space volume considerations.