Abstract:In this paper, the oscillation of the Poisson semigroup associated with parabolic Bessel operator L=?t-Δx-x2(1/4-μ2)(μ〉-1) is considered. The oscillation operator O(PLτ) is bounded from Lp(?2)(1〈p〈∞) into itself, from L1(?2)into weak-L1(?2), and bounded from Lc(∞)(?2) into BMO(?2) is proved by the parabolic semigroup method and Calderón-Zygmund theory. In the case p=∞, it is showed that the range of the image of the oscillation O(PLτ) is strictly smaller than the range of a general singular operator in some sense.