Soil air permeability is an important parameter to characterize convective gas transport through the soil gas phases. However, current air permeability measurements have limitations, specifically in Andisols, which are highly aggregated and often shrink during drying processes. Determining the air content at different tension gradient points by drying is also time consuming because experiments have to reach several steady-state conditions. Thus, the objective of this research was to demonstrate an unsteady-state air permeability measurement method with confined sleeve pressure. Furthermore, the effects of confined pressure and air leakage on the measurement of air permeability were determined using an Andisol across a wide range of soil water and air contents. Under confined pressure, the air flow rates at air contents of 0.2, 0.4, and 0.6 m3 m−3 and soil bulk density of 0.75 Mg m−3 were 5.8, 2.3, and 0.8 times higher, respectively, than those under unconfined pressure. Using the unsteady-state air permeability measurements method on the Andisol, our results show that the interaggregate region had air contents in the range from 0.13 to 0.25 m3 m−3, with air permeability ranging from 12.6 to 54.8 μm2. Conversely, the intraaggregate region had air contents ranging from 0.25 to 0.65 m3 m−3, with air permeability ranging from 54.8 to 81.5 μm2. The intraaggregate air permeability increased only slightly due to less space in the aggregate.