Time-of-flight(TOF) mass spectra of molecular butanone clusters were measured under the irradiation of photons at 355 and 118 nm. Butanone molecular parent ion and several series of butanone cluster fragments such as (CHCOCH)H, (CHCOCH)CHCO were observed. Odd-even variation pattern in the intensity of (CHCOCH)CHCO and the neutral clusters (CHCOCH) based on the consideration of butanone cluster dissociation mainly by losing a radical CH. The stability variation of the neu- tral clusters calculated via the HF-B3LYP method based on DFT is in agreement with the observed phenomena expe- rimentally, indicating (CHCOCH)(n+1=5,7) with a ring structure are with higher stability over the adjacent even-number clusters.