High-silica Beta zeolites, typically synthesized by hydrothermal synthesis with the assistance of F - or seeds, are highly important in volatile organic compounds (VOCs) adsorption. Fluoride-free or seed-free synthesis of high-silica Beta zeolites attracts great attention. Herein, highly dispersed Beta zeolites with a size of 25-180 nm and Si/Al ratios of 9-∞ were successfully synthesized by a microwave-assisted hydrothermal strategy. We have for the first time revealed that microwave irradiation can induce the formation of hydroxyl free radicals (˙OH), promoting the formation of the Si-O-Si bond. Thanks to the high total surface area, pore volume, and excellent hydrophobicity, the as-prepared pure-silica Beta zeolite presents a higher toluene adsorption capacity in VOCs adsorption compared to other pure-silica Beta zeolites prepared by traditional methods. This work provides a facile avenue for fluoride-free and seed-free synthesis of nanosized high-silica zeolites, promising their important applications in VOCs adsorption.