We present photoabsorption oscillator strengths for C3H6 molecules with emphasis on the difference between isomers, cyclopropane and propylene. We use an iterative numerical method based on the time-dependent local density approximation with continuum, which we have recently developed. The oscillator strengths for the two isomers differ at photon energies above their ionization thresholds. The magnitude and the shape of the oscillator strength distribution are in good agreement with recent experiments. The differences between the isomers arise from difference in symmetry of electronic states and different behaviors of continuum excitations. (C) 2003 Elsevier Science B.V. All rights reserved.