The present investigation deals with the comb-like complexes made of poly(ethylene imine) (PEI) and stearic acid (SA) or oleic acid (OA). On cooling the mixture of dimethylformamide solutions of PEI and carboxylic acid to room temperature, the corresponding complexes were phase-separated and precipitated. Structures and liquid crystallinity of the PEI-OA and PEI-SA complexes were studied by means of various techniques. It was confirmed by infrared spectroscopy studies that the carboxylic acid molecules are linked by ionic bonds to form the comb-like complexes. The complexes give a narrow peak at 2 theta = 2 degrees-3 degrees in their wide-angle X-ray diffractograms, indicating that the side aliphatic chains are packed in layer structure with a spacing of 3.2-4.4 nm. In spite of the rather weak secondary valence force between an imine group of PEI and a carboxylic end group, the layer structures of the complexes are maintained even at the temperatures above the melting point of the side chains. Both of the comb-like complexes form optically positive spherulitic textures from the melt, indicating that the layer structures are oriented concentrically and consequently side aliphatic chains are oriented in a radial direction. Concentric arrangement of the layer structure is characteristic of the smectic-type liquid crystal. These results suggest the liquid crystallinity of the comb-like complexes are made of PEI and carboxylic acid.