Abstract: The present invention provides a method for separating and preparing a therapeutic agent for chronic myelogenous leukimeia capable of effectively inhibiting growth of T315I, which is known as a mutation of a BCR-ABL fusion gene that causes chronic myelogenous leukemia, comprising the steps of: 1) preliminary extracting by adding ethyl acetate to finely chopped bark of Liriodendron tulipifera L., adding butanol to an extracted fluid for layer-separating an ethyl acetate layer and a butanol layer, removing the butanol layer, and decompression-condensing the remainder to obtain a crude extract; and 2) adding a C1-C3 lower alcohol aqueous solution and n-hexane to the obtained crude extract, removing lipids and water insoluble material dissolved in the n-hexane layer, and obtaining and separating a lower alcohol aqueous solution layer to separate and refine highly pure epi-tulipinolide and costunolide.