Complexation behavior of deoxycholic acid was studied for poly(oxy-ethylene), poly(propylene oxide), poly(tetrahydrofuran), and several poly(oxyethylene) derivatives with various chain lengths. The complexes were obtained for poly(oxyethylene) with an average molecular weight greater than 200 (average degree of polymerizationn= 4). In spite of very short ethylene oxide chains, poly(oxyethylene) monostearate and poly(oxyethylene) mono-p-nonylphenyl ether withn= 2 formed the complexes. The unit cells of all complexes corresponded to the orthorhombic crystal which is most commonly observed for the complexes with low molecular weight compounds. Dimensionain the complexes of poly(propylene oxide) and poly(oxyethylene) mono-p-nonylphenyl ether withn= 2 and 5 was larger than those in other complexes, whilebandcdid not differ much. Most of the complexes exhibited an increase in the melting points with increasing length of the polymer chains, while the melting points of poly(oxyethylene) monostearate complexes decreased withnand those of poly(oxyethylene) mono-p-nonylphenyl ether showed a minimum betweenn= 5 andn= 10.