Summary: This research is to study the potential of using polystyrene nanoparticles and chitosan solution to increase the anti-bacterial activity on cotton fabrics prepared by a conventional pad-dry-cure method. Firstly, cotton fabrics were coated with chitosan solutions at the concentrations of 0.1, 0.5, and 1.0 (%w/v) and tested for the antibacterial property which was determined by clear zone measurement and viable count assay using Escherichia coli (ATCC 25922) as a tested microorganism. The results showed that, the percentage bacterial reductions were 87.2, 86.3, and 48.5%, respectively, when the cotton fabrics was coated only with chitosan solution. When polystyrene nanoparticle solution was coated onto cotton fabrics prior to coating with chitosan solutions at the concentrations of 0.1, 0.5, and 1.0 (%w/v), the percentage bacterial reductions were 90.3, 90.8, and 65.5%, respectively. This indicated that coating the cotton fabrics with polystyrene nanoparticles prior to chitosan coating would remarkably increase the antibacterial activity. The scanning electron micrographs showed that polystyrene nanoparticles were aggregated and inserted in between the interfiber spacings. The thin film of chitosan was also observed on the surface of cotton fabrics and hydrophobic property of the fabrics was tested via contact angle measurement.