Information on rumen disappearance of phytonutrients is needed to assess their potential post-ruminal effects in ruminants. The objective of this study was to investigate rumen disappearance rates and escape of 2 phenolic phytonutrients, carvacrol (CAR) and anethole (ANE), in 2 experiments using dairy cows. Each experiment involved 4 mid-lactation Holstein cows (average ± SD; 26 ± 2.8 kg/d DMI; 41 ± 3.1 kg/d milk yield; 134 ± 8.5 d in milk) and consisted of 3, 14-d experimental periods. In Exp. 1, CAR was administered into the rumen of the cows at 3 doses: 0.5, 1.0, and 2.0 g/cow in periods 1, 2, and 3, respectively. Chromium-EDTA was used as a rumen fluid passage rate marker. On the first day of each experimental period, CAR and Cr-EDTA solutions were administered intraruminally in each cow through the rumen cannula at the time of feeding. Rumen fluid samples were collected from 4 locations in the rumen at 0 (background), 0.5, 1, 2, 6, 12, and 24 h after CAR administration. The same procedure was conducted for ANE in Exp. 2; ANE doses were the same as for CAR. Concentration of CAR and ANE in ruminal fluid were fitted to a single exponential decay model (y = a × exp[−b × x]). The rate of degradation of CAR or ANE was found as: k_CAR or k_ANE − k_Cr, where k_Cr is the slope of decline in Cr concentration in ruminal fluid (on average 0.20 ± 0.07 h⁻¹) and k_CAR and k_ANE are slopes of decline in CAR and ANE concentrations, respectively. Rumen escape was calculated as: k_Cr ÷ (k_Cr + kd), where kd is the rate of degradation of CAR or ANE. Rumen disappearance rates of CAR were 0.29 ± 0.05, 0.31 ± 0.07, and 0.34 ± 0.08 h⁻¹ and those of ANE were 1.43 ± 0.29, 1.52 ± 0.43, and 1.42 ± 0.38 h⁻¹ for the 0.5, 1.0, and 2.0 g/cow doses, respectively. The rates of degradation of CAR were estimated at 0.15 ± 0.07, 0.13 ± 0.06, and 0.09 ± 0.07 h⁻¹ and those of ANE were 1.24 ± 0.27, 1.31 ± 0.41, and 1.24 ± 0.43 h⁻¹, respectively. Rumen escape of CAR was 47.2, 59.3, and 73.8% and that of ANE was 13.7, 14.8, and 14.2%, respectively. In this study, rumen escape of CAR and ANE in lactating dairy cows was from 13.7 to 73.8%, depending on dose and compound.