To get insight into the air entrainment process from a Taylor bubble in a vertical tube, we measured the gas loss from a Taylor bubble that was held stationary in a downward liquid flow. Also, we measured the void fraction in the downward bubbly flow below the Taylor bubble, as well as the radial void fraction distribution in this region. We varied the Taylor bubble length, the liquid flow rate approaching the bubble, and the turbulence level of this flow. The experiments strongly indicate that the entrainment flux is related to the presence of turbulence in the liquid film surrounding the Taylor bubble.