Durable and regenerable antibacterial properties have been achieved on cotton and cotton-containing fabrics using an innovative finishing method. The chemistry of the functional finishing is based on a redox reaction of halamine compounds. Here, the chemical and structural analysis of 5,5-dimethylhydantoin (MDMH) are addressed and some questions are answered. Instrumental and chemical analysis such as FTIR spectrometry and nitrogen and chlorine elemental analyses were utilized in the study. The results of FTIR and elemental analyses confirmed the existence of hydantoin rings on cellulose chains and the stability of the chemical linkage between the hydatoin ring and the polymer chain. The results of chemical and structural analysis also explain why polyester/cotton samples tend to have better biocidal activity than all-cotton fabrics.