High-resolution transmission electron microscopy and energy-dispersive X-ray analysis carried out on indium oxide nanotubes grown by a chemical vapor deposition technique show the presence of indium metal segments along the indium oxide (IO) nanotube axis having one end closed. A real-time HRTEM video in continuous mode imaging has been carried out to study the directional flow of liquid indium. Electron-beam-induced heating results in the increase in indium vapor pressure and desorption of gases at the closed end of the IO nanotubes. This buildup of differential pressure between open and closed columns leads to the flow of indium away from the closed end of the IO nanotube. Interestingly, the indium flow rate was observed to decrease from 2.8 to 0.3 nm/s with a corresponding decrease in the nanotubes’ diameter from 138 to 38 nm. This study indicates that the wetting properties of the liquid−host nanotube interface critically decides the fluid dynamics at nanoscale, and depending upon the interfacial properties, enhancement or retardation of flow can be observed on the reduction of the nanotube diameter.