In this study, the commercial organophosphorus compound Pyrovatex CP New was used as a flame retardant for cotton fabric. Citric acid and a modified dihydroxy ethylene urea (DHEU) labelled Knittex FFRC were used as crosslinking to increase the flame-retardant laundering durability of treated cotton fabric. There have been some studies showing that Chitosan has the potential to improve flame retardancy and laundering durability of flame retardant treated cotton fabric. Thus, Chitosan, which has the molecular weight of 2.600 (water soluble) and the deacetylation degree of approximately 75%, is added to finishing solution for flame retardant treatment of cotton fabric. The padding-drying-curing method was used in this study. After treatment, all samples were examined to determine the chemical absorption level. The 45° flammability test characteristics and LOI value of untreated and treated samples after different number of washing cycle were determined to assess the flame retardancy of the treated fabric and its laundering durability. In addition, to assess the impact of this treatment on the mechanical strength and ecology of the fabric, the tensile strength and free formaldehyde content of the treated fabric were also evaluated