Bismuth nano-Hall sensors with dimensions ∼50 nm × 50 nm were fabricated using a combination of optical lithography and focused ion beam milling. The Hall coefficient, series resistance and optimum magnetic field sensitivity of the sensors were 4×10-4 Ω/G, 9.1 kΩ and 0.8 G/√Hz, respectively. A 50 nm nano-Bi Hall sensor was installed into a room temperature scanning Hall probe microscope and successfully used for directly imaging ferromagnetic domains of low coercivity garnet thin films.