A series of gold nanoparticles (AuNPs) with controllable size were prepared from immobilized gold-containing ionic liquid on SBA-15 (AuCl_me-Im@SBA-15) at room temperature. AuNPs size and shape could be controlled inside porous SBA-15 in the presence of immobilized 1-methyl-3-(3-trimethoxysilyl- propyl)-imidazolium chloride by controlling a concentration and a feed rate of a reducing agent NaBH4. The smallest AuNPs with the average size of 1.6 nm was obtained at a fixed feed rate of 0.2 ml/min with 4 mM NaBH4. The transformation of AuNPs shape from spherical to capsule-like NPs was observed at low feed rate of 0.04 ml/min. The prepared AuNPs catalysts were characterized by TEM, XPS, FTIR, and XRD. The catalyst with the smallest NPs, AuNP (1.6 nm)_me-Im@SBA-15, exhibited the highest catalytic performance in p-nitrophenol hydrogenation reaction at room temperature. Moreover this catalyst was reusable up to four recycle processes.