Solid-liquid extraction of the taxane compounds in yew needles is carried out with methanol. The concentration of each component in the raffinate is estimated from the observed concentration in the extract and material balance equations with a solvent-permeation model that solvent permeates the solid. The obtained distribution coefficient is found to be independent of the particle size. It suggests a possibility that the extract is in equilibrium with the liquid solution in the raffinate. Based on the experimental results, the effect of operating conditions on separation performance of countercurrent-multistage extraction is studied by using the ideal stage calculation.