For the first time, using wet cell in a liquid environmental transmission electron microscopy (LETEM), we have successfully generated highly stable oxygen nanobubbles with diameter 5~7 nm by decomposition of 0.02% H 2 O 2 on Pt/CNT nanocomposite. The nucleation, growth and stability of those nanobubbles have been characterized. Along with this, we also have studied the variation of the internal pressure with average radius of stable nanobubbles with respect to time.