Owing to their excellent photoluminescence (PL) properties in a narrow linewidth below 30 nm and high photoluminescence quantum yield (PLQY), organometal halide perovskite nanocrystals (PeNCs) are promising photonic sources for wide-color gamut displays. However, with a top-down approach, luminescent PeNCs comparable to those prepared through bottom-up synthesis is still a significant subject, including the optimization of milling processes. Herein, we propose a novel and simple ultrasound-assisted bead milling process based on the characteristics of facile crystallization. During the milling process, irradiated ultrasounds disperse milling beads that facilitate an intense collision between the beads and the perovskite precursors. Thus, this bead milling can be easily performed without planetary ball milling, and it provides brightly luminescent colloidal PeNCs with high PLQY. We established that mechanochemical conditions significantly enhance the optical properties by exploring various milling conditions. Furthermore, the color adjustment can be realized by changing the halide composition. Therefore, this novel milling process has great potential and versatility for preparing diverse perovskite nanomaterials for optoelectronic applications.