Equations used to predict pressure drop in low-velocity slug-flow are derived and a new experimental method is presented to measure the properties of slug (actually an aerated material bed). Based on the measured properties, the derived equations can predict pressure drop in low-velocity slug-flow pneumatic conveying accurately. The equations and method can be applied to bulk solid materials with regular, irregular and/or unusual physical properties (e.g. different shape, density and size distribution), as long as they are good candidates for this mode of pneumatic conveying. Experiments show that the results predicted by this method can guide the design and field operation.