The high-resolution photo-absorption cross-section of CH3CHO has been measured using synchrotron radiation in the range 3.0-11 eV (413 nm > lambda > 113 nm). Electronic state assignments have been suggested for each of the observed absorption bands incorporating both valence and Rydberg transitions. Valence transitions to the singlet and triplet states are assigned. Six Rydberg series have been assigned converging to the ionisation energy limit 10.229 eV. Rydberg orbitals of each series are classified according to the magnitude of the quantum defect (6). The measured VUV crosssections are used to derive the photolysis rates of acetaldehyde in the terrestrial atmosphere. (C) 2003 Elsevier B.V. All rights reserved.