Chitosan quaternary ammonium salt is utilized in water treatment for its strong positive charge, effectively flocculating and removing suspended solids, organic matter, dyes, and heavy metals from wastewater. Its antimicrobial properties make it suitable for food preservation as a natural preservative, inhibiting bacterial and fungal growth, and forming edible films or fruit coatings to extend shelf life. In cosmetics and skin care products like creams and serums, it offers moisturizing, film-forming benefits, and helps reduce acne. In agriculture, it functions as a seed coating agent and biopesticide, promoting plant growth and protecting against pathogens. In pharmaceuticals, it enhances drug absorption, particularly for poorly water-soluble drugs, due to its good water solubility and ability to permeate biological membranes, and is applied in controlled drug delivery systems such as microspheres and films for sustained release.