Stimulated Brillouin scattering offers a broad range of applications, including lasers, sensors, and microwave photonics, most of which require strong Brillouin gain within a narrow bandwidth. Here, we experimentally report the first measurement of stimulated Brillouin scattering in silica optical nanofibers from both hybrid and surface acoustic waves. Using a pump-probe technique in the radio-frequency domain, we measured a Brillouin gain as high as 15 m−1W−1 and linewidth to 16 MHz for the L03 hybrid acoustic mode near 9 GHz using a 990-nm diameter nanofiber. This gain is 65 times larger than the highest gain obtained in standard single-mode fibers. Additionally, we report a Brillouin gain of up to 5 m−1W−1 from surface acoustic waves around 5 GHz. We further demonstrate a nanofiber-based Brillouin laser with a threshold of 350 mW. Our results create opportunities for advanced Brillouin-based applications utilizing optical nanofibers.