The rate constants for the Cl atom reaction with three branched ketones have been measured at 298 ± 2 K and 760 Torr using the relative rate method in the absence of NO. The rate constants values obtained (in units of 10− 10 cm3/(molecule·sec)) are: k(2-methyl-3-pentanone) = 1.07 ± 0.26, k(3-methyl-2-pentanone) = 1.21 ± 0.26, and k(4-methyl-2-pentanone) = 1.35 ± 0.27. Combining the chemical kinetic data obtained by this study with those reported for other ketones, a revised Structure Activity Relationship (SAR) parameter and R group reactivity (kR) of R(O)R′ and CHx (x = 1, 2, 3) group reactivity (kCHx) toward Cl atoms were proposed. In addition, the products from the three reactions in the presence of NO were also identified and quantified by using PTR-ToF-MS and GC-FID, and the yields of the identified products are: acetone (39% ± 8%) + ethanal (78% ± 12%), 2-butanone (22% ± 2%) + ethanal (75% ± 10%) + propanal (14% ± 1%) and acetone (26% ± 3%) + 2-methylpropanal (24% ± 2%), for Cl atoms reaction with 2-methyl-3-pentanone, 3-methyl-2-pentanone and 4-methyl-2-pentanone, respectively. Based on the obtained results, the reaction mechanisms of Cl atoms with these three ketones are proposed.