Biopolymers are suitable replacement materials for different chemical processes. In this work, silk yarns were treated with different chitosan concentration and then dyed with mono and bi-functional reactive dyes. The color yield, color difference and color fastness to light and washing of the dyed silk yarns were evaluated. Also, the effects of chitosan concentration, type of the reactive dyes on dye uptake of samples were studied. The bi-functional reactive dye has a high adsorption compared to mono-functional ones. The silk yarn treated with 3% chitosan had higher K/S values, washing and light fastness. The effects of chitosan on the antibacterial properties of silk yarns against two kinds of bacteria: Staphylococcus aureus and Escherichia coli were investigated. The treated silk samples were found to have antibacterial potential due to the antibacterial property of chitosan. Scanning electron microscopy (SEM) photographs reveal the deposition of chitosan on the treated yarns. Washing durability, handle properties, and yellowness of treated and dyed samples were also investigated.