Ultrafast electronic relaxation following 9.3 eV photoexcitation of gaseous acetone was investigated with time-resolved photoelectron imaging spectroscopy. An intense photoionization signal due to a transition from the 4(1)A(1)(pi,pi*) state to the D-1 (pi(-)(1)) cationic state diminishes within 50 fs, owing to vibrational wave packet motion leaving our observation energy window. Additional photoionization signals were assigned to transitions from Rydberg states with principal quantum numbers of 3-8 to the D-0(n(-1)) cationic state, created by strong vibronic couplings with the bright 4(1)A(1)(pi,pi*) state. The deactivation processes of the 4(1)A(1)(pi,pi*) and Rydberg states are discussed based on their decay profiles obtained from a time-energy map of photoelectron kinetic energy distributions.