The methods to synthesize water soluble quaternary ammonium chitosan derivatives and the feasibility to use them as antimicrobial finishing agents for textiles were studied. Chitosan with 87% degree of deacetylation was purified and reacted with a solution containing methyl iodide, sodium hydroxide, and sodium iodide in N-methyl-2-pyrrolidone at different reaction conditions to synthesize N-trimethyl chitosan ammonium iodide (TMCI). Pure TMCI was obtained by reprecipitation and soxhlet extraction. To obtain a stable chloride salt form of N-tri-methyl chitosan ammonium chloride (TMCC), the counterion $I^-$ was exchanged with $Cl^-$ by reprecipitating aqueous TMCI solution in HCl/ethanol solution. The proper syntheses of TMCI and TMCC were confirmed by $H^l-NMR$ and FT-IR spectroscopies. Degrees of substitution in TMCI and TMCC were calculated from iodide and chloride contents obtained by a combustion flask method, respectively. The degree of substitution of TMCI was varied with reaction conditions and TMCI became water soluble at the degree of substitution higher than 0.55. Cotton fabrics were treated with various concentrations of aqueous TMCI and TMCC solutions to test feasibility of them as antimicrobial finishing agents. The antimicrobial activity of TMCI- and TMCC-treated cotton fabrics were measured by AATCC 100 using Staphylococcus aureus (A.T.C.C. No. 6538) and Klebsiella pneumoniae (A.T.C.C. No.4352). Results showed that the bacteria reduction was almost 100% when treated with solutions at concentrations above 0.025% for both cases.