The room-temperature synthesis of beta-Ga2O3 nanocrystal was examined by coupling two biomimetic crystallization techniques, enzymatic peptide nanoassembly templating and aggregation-driven crystallization. The catalytic template of peptide assembly nucleated and mineralized primary beta-Ga2O3 crystals and then fused them to grow single-crystalline and monodisperse nanoparticles in the cavity of the peptide assembly at room temperature. In this work, the peptide assembly was exploited as a nanoreactor with an enzymatic functionality catalyzing the hydrolysis of gallium precursors. In addition, the characteristic ring structure of peptide assembly is expected to provide an efficient dehydration pathway and crystallization control over the surface tension, which are advantageous for beta-Ga2O3 crystal growth. This multifunctional peptide assembly could be applied for syntheses of a variety of nanomaterials that are kinetically difficult to grow at room temperature.