The lubrication properties of two commercial-grade magnesium stearates were studied. Their moisture contents and crystal structures were similar. There were minor differences in their fatty acid composition, but the differences did not affect the lubrication properties. The lubrication properties correlated with particle size distributions and specific surface area. The effect of these parameters was further studied with unmilled and milled chemically pure magnesium stearate. Milling decreased the particle size and increased the specific surface area. In both cases, the batch with a smaller particle size and larger specific surface area had considerably better lubricity.