The kinetics and mechanism of the reaction of C₆H₅ with CH₃CHO have been investigated experimentally and theoretically. The total rate constant for the reaction has been measured by means of the cavity ring‐down spectrometry (CRDS) in the temperature range 299–501 K at pressures covering 20–75 Torr. The overall bimolecular rate constant can be represented by the expression k=(2.8±0.2)×10¹¹ exp[−(700±30)/T] cm³ mol⁻¹ s⁻¹, which is slightly faster than for the analogous C₆H₅+CH₂O reaction determined with the same method in the same temperature range. The reaction mechanism for the C₆H₅+CH₃CHO reaction was also explored with quantum‐chemical calculations at various hybrid density functional theories (DFTs) and using ab initio high‐level composite methods. The theories predict that the reaction may occur by two hydrogen‐abstraction and two addition channels with the aldehydic hydrogen‐abstraction reaction being dominant. The rate constant calculated by the transition state theory for the aldehydic hydrogen‐abstraction reaction is in good agreement with the experimental result after a very small adjustment of the predicted reaction barrier (+0.3 kcal mol⁻¹). Contributions from other product channels are negligible under our experimental conditions. For combustion applications, we have calculated the rate constants for key product channels in the temperature range of 298–2500 K under atmospheric‐pressure conditions; they can be represented by the following expressions in units of cm³ mol⁻¹ s⁻¹: k_1,cho=8.8×10³ T^2.6 exp(−90/T), k_2,ch3=6.0×10¹ T^3.3 exp(−950/T), k_3a(C₆H₅COCH₃+H)=4.2×10⁵ T^0.6 exp(−410/T) and k_3b(C₆H₅CHO+CH₃)=6.6×10⁹ T^−0.5 exp(−310/T).

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