Cotton fibers were pretreated with 5.4-N sodium hydroxide in an ethanol—water (volume ratio, 30: 70) mixture and then cyanoethylated with acrylonitrile. The crystalline structure of the cyanoethylated cotton fibers was investigated by the X-ray method and compared with that of the cotton fibers, pretreated with 5.4-N aqueous sodium hydroxide and cyanoethylated under the same conditions. The presence of ethanol in the sodium hydroxide solution resulted in the increased accessibility of cellulose and a remarkable broadening of the X-ray profile. Cotton fabrics were also treated with alkali—acrylonitrile in the presence of ethanol; their physical properties are discussed.