The relative rate coefficient for the gas-phase reaction of 3-hydroxy-3-methyl-2-butanone (3H3M2B) with Cl atoms was determined under atmospheric conditions (298 +/- 2 K, 720 +/- 2 Torr). The products of the reaction were identified and quantified. This work provides the first kinetic and mechanistic determinations of the gas-phase reaction of Cl atoms with 3H3M2B. The rate measurements and the products studies were performed in two simulation chambers coupled to the gas chromatography mass spectrometer (GC MS) and the Fourier transform infrared (FTIR) techniques, respectively. The obtained average rate coefficient was (1.13 +/- 0.17) X 10(-1) cm(3) molecule(-1) s(-1) using propene and 1,3-butadiene as reference compounds. The major primary reaction products observed in this study were (with % molar yields): acetic acid (42.6 +/- 4.8) and 2,3-butanedione (17.2 +/- 2.3). Results and mechanism are discussed in terms of the structure reactivity relationship and compared with the reported reactivity with the other atmospheric oxidants. The atmospheric implications derived from this study are discussed as well.