Woven cotton fabric was chemically modified by a self-made cationic modifying chicken feather keratin agent (named WLS-10). The dyeing dynamics property and the dyeing effectiveness of the modified cotton fabric dyed with reactive dyes in the absence of salt were explored and compared with that of the unmodified cotton fabric dyed with reactive dyes in the presence of salt. The structures of the WLS-10 agent and the modified cotton fabric were characterized with Fourier transform infrared spectroscopy and scanning electron micrographs. The results showed that the dyeing rate of the WLS-10 modified cotton was higher than that of unmodified cotton dyed with reactive dyes, despite the addition of large amounts of salt in the latter case. In addition, the chemical structure and the surface morphological structure of the modified cotton fabric were different from that of the unmodified cotton fabric.