Abstract The impact of ultra-fine coal particles on the flotation of coarse coal particles is investigated in this work. Flotation experiments of three coal samples were conducted. The results showed that the recovery of coarse coal particles (> 74 μm) decreases when low-ash ultra-fine coal particles are added into coal samples, whereas the addition of high-ash ultra-fine coal particles has very slight impact on it. Measurements of contact angle and wetting heat were conducted to examine the interaction between ultra-fine coal particles and flotation reagents. The results showed that low-ash ultra-fine coal particles have very strong adsorption to both collector and frother, whereas high-ash ultra-fine coal particles have strong adsorption to collector but weak adsorption to frother, which indicates that frother may play a more important role in the recovery of coarse coal particles.