The effect of frothers on the degree of entrainment is important for selective flotation, but the mechanism underpinning the effect is still poorly understood. In this study, gangue only batch flotation tests were performed using fully liberated quartz in a 3.5 L conventional Agitair flotation cell, and the degree of entrainment was assessed at different frother concentrations using Dowfroth 250 and MIBC. Results show that the effect of frothers on the degree of entrainment was the consequence of changes in the upward liquid motion across the pulp/froth interface. The frothers changed the bubble size, resulting in a change in liquid content and liquid velocity at the interface. The change in interface liquid velocity then changed the drag force which determined the motion of a particle against the downward gravitational force on the particle due to its weight, resulting in a change in the amount of hydrophilic solid particles following the water phase and being recovered in the water phase, and hence the degree of entrainment. The results also suggest that the classification of hydrophilic solid particles occurred at the interface region. (C) 2016 Elsevier Ltd. All rights reserved.