The diffusion coefficients of benzonitrile in the CO2-expanded ethanol at the temperatures of (303, 313, and 323) K and the pressures ranging from (1.49 to 9.79) MPa were measured by the chromatographic peak broadening technique. The benzonitrile diffusion coefficients in the CO2-expanded ethanol were observed to increase with increasing CO2 mole fraction in ethanol. For a fixed CO2 mole fraction in ethanol, the benzonitrile diffusion coefficients were found to increase with increasing temperature at a fixed pressure and to decrease with increasing pressure at a fixed temperature. The measured diffusion coefficients could be correlated well by the modified Wilke-Chang equation with an average absolute deviation of 5.1%.