The photoionization of acetone seeded in helium is studied by time-of-flight mass spectrometry using a 25 ns, 532 nm Nd: YAG laser with intensity in the range of 10(10)-10(11) W/cm(2). Multiply charged ions of OP+ (p = 2-4) and Cq+ (q = 2-4) of tens of eV have been observed when the laser beam irradiates the most dense part of the pulsed molecular beam. The intensity and the kinetic energy of the multiply charged ions increase with the increasing of the laser energy. An electron re-scattering and re-colliding ionization model is proposed to explain the appearance of the multiply charged ions under such low laser intensity.