Electronic Journal of Differential Equations, Vol. 2012 (2012), No. 175, pp. 1-9. Title: Spectral mapping theorem for an evolution semigroup on a space of vector-valued almost-periodic functions Author: Olivia Saierli (West Univ. of Timisoara, Romania) Abstract: We give some characterizations for exponential stability of a periodic evolution family of bounded linear operators acting on a Banach space in terms of evolution semigroups acting on a special space of almost periodic functions. As a consequence, a spectral mapping theorem is stated. Submitted May 11, 2012. Published October 12, 2012. Math Subject Classifications: 47A05, 47A30, 47D06, 47A10, 35B15, 35B10. Key Words: Periodic evolution families; uniform exponential stability; boundedness; evolution semigroup; almost periodic functions.