A pulse-radiolysis system was used to measure absolute rate constants for the reactions of CH₃C(O)O₂ radicals with NO and NO₂ at 295 K and 1000 mbar total pressure of SF₆. When the rate of formation and decay of NO₂ using its absorption at 400.5 and 452 nm were monitored, the rate constants k(CH₃C(O)O₂ + NO) = (2.0 ± 0.3) × 10^-11 and k(CH₃C(O)O₂ + NO₂) = (1.0 ± 0.2) × 10^-11 cm³ molecule^-1 s^-1 were determined. Long path-length Fourier transform infrared spectrometers were used to study the rate-constant ratio k(CH₃C-(O)O₂ + NO)/k(CH₃C(O)O₂ + NO₂) in 6-700 Torr total pressure of N₂ diluent at 243-295 K. At 295 K in 700 Torr of N₂ diluent k(CH₃C(O)O₂ + NO)/k(CH₃C(O)O₂ + NO₂) = 2.07 ± 0.21. The results are discussed in the context of the atmospheric chemistry of acetylperoxy radicals.