The rate constants and products for the reactions of atomic Cl and O3 molecule with 3-methyl-3-buten-2-one (MBO332) and 3-methyl-3-penten-2-one (MPO332) were determined in a 100 L Teflon chamber at 293 ± 1 K and atmospheric pressure. For MBO332 and MPO332, the rate constants measured with atomic Cl were (2.38 ± 0.26) × 10(-10) and (3.00 ± 0.34) × 10(-10) cm(3) molecule(-1) s(-1) using the relative rate method. Using the absolute rate method, the rate constants with O3 measured were (1.18 ± 0.21) × 10(-17) and (4.07 ± 0.45) × 10(-17) cm(3) molecule(-1) s(-1). The products of these reactions were investigated by the proton-transfer-reaction mass spectrum (PTR-MS). The results indicated that the major products observed in the atomic Cl reaction were formaldehyde together with chloroacetone for MBO332, and acetaldehyde and CH3C(O)C(O)Cl for MPO332. For O3 reactions, butanedione and formaldehyde were the main products of MBO332, while butanedione and acetaldehyde were the main products of MPO332. Possible reaction mechanisms were proposed and discussed and the atmospheric implications of these reactions were also discussed.