Abstract: Two kinds of magnetite concentrates from Pilbara in Australia and an area in the northeast in China were used to explore the effect of wettability, which depends on particle size, on ballability. Capillary osmosis equipment of a horizontal plate was constructed based on the equation Washburn. To investigate the effect of particle size and wettability of ultrafine magnetite concentrates on ballability, ballability, balling test, and performance test were performed. The results suggest that ultrafine particle size and wettability strongly affect ballability. Its better wettability on account of particle ultrafine size characteristic is beneficial to improve its compressive strength. However, a narrow ultrafine particle-size distribution will limit the improvements in ballability, because it affects the capillary radius.