Here, we present a series of experimental studies to encapsulate ultrasmall gold nanoparticles into mesoporous metal oxide via an in situ self-assembly method. Notably, the 2.0Au@mZnO catalyst (similar to 2.0 nm gold nanoparticles loading on mesoporous ZnO nanospheres) shows excellent catalytic activity for indane oxidation (120 degrees C, conversion 88.5%) and affords much high turnover frequencies (9521 h(-1)). The catalytic activity of these gold-based catalysts was found to be correlated with the size of gold nanoparticles and the types of metal oxide supports. With a decrease in gold nanoparticle size, the catalytic conversion efficiency of indane oxidation increased. In addition, such catalysts possessed high thermal and chemical stability and could be reused more than 10 times without a remarkable loss of catalytic activity.