HKUST-1 (HKUST = Hong Kong University of Science and Technology) is one of the most recognized metal-organic frameworks (MOFs) based on copper and trimesate, extensively studied for a variety of applications, such as gas storage, separation, adsorption, electrocatalysis, drug delivery, sensor and photodegradation, etc. In this work, we introduce a novel nanofused HKUST-1, referred to as N-CuBTC (BTC = trimesate), which has been synthesized with the hydrothermal method at room temperature (typical synthesis temperature is from 80~120 °C). The resulting N-CuBTC features an irregular particle morphology, with numerous crystals clustering together and edges that have fused, creating a hierarchical pore structure. In contrast to the traditional micro-sized octahedral HKUST-1 (named as M-CuBTC), N-CuBTC displays a unique clumped morphology, where the HKUST-1 crystals are seamlessly integrated into a cohesive structure. This innovative formation significantly enhances mass transfer capabilities and porosity accessibility. Consequently, N-CuBTC demonstrates markedly improved catalytic performance in the cyanosilylation of aldehydes.