Antimicrobial finish of cotton fabrics using 30% aqueous ethanol solution of trimethoxysilypropyl group introduced poly(hexamethylene guanidine hydrochloride) (PHGS) was studied. Cotton fabrics were treated with PHGS solution by pad-rry-cure or by simple pad-dry process at various curing or drying conditions and the bacterial reduction of them after repeated launderings were investigated. The treated fabrics were also dyed with bromophenol blue(BPB) and their reflectances were measured to estimate residual amounts of PHGS in the fabric after repeated launderings. By calculating K/S values using Kubelka-Munk equation, we could predict the antimicrobial activity of the sample without measuring time-consuming bacterial reduction. The fabrics treated with 1% PHGS and dried at and above 8$0^{circ}C$ for at least 3 minutes showed almost 100% bacterial reduction and good durability to repeated launderings. All the cured samples after drying at 10$0^{circ}C$ showed excellent antimicrobial activity after 10 repeated launderings regardless of curing conditions. But samples dried below 8$0^{circ}C$ without curing showed little lower antimicrobial activity before laundering. They also showed much lower laundering durability compared with the one died above 8$0^{circ}C$. Ethoxy groups in PHGS which changed from methoxy groups because of ethanol in solvent presumably reacted with hydroxy group in cotton to make chemical primary bonds by simple drying above certain temperature. Therefore no curing process with high temperature was needed. Just simple drying of the padded fabric gave excellent laundering durability. This simple treating process without curing must be a excellent advantage of PHGS in commercial application.