Because of their special properties such as environment-friendly and biodegradability characteristics, poly lactic acid (PLA) fibers have many applications in various fields, especially in medicals such as the surgical suture, suture, bed cover, hospital gown and implants. On the other hand, textiles are favorable environment for growth of microorganisms. So, depending on their applications, an appropriate antimicrobial treatment to prevent bacterial growth should be carried out. For many antibacterial compounds, in order to develop its antimicrobial properties, some time is required and these materials are said to be slow in antibacterial properties. The good wash stability, rechargeable and fast performance properties of N-halamines have led to the use of these materials as antimicrobial agents for the medical textiles. However, to modify the chemical structure of polymers, especially for improvement of the fibers properties, the reactive extrusion process due to advantages such as non application of solvents, simplicity of product isolation, short reaction times and continuous process have been used over the last three decades. In this thesis, radical melt graft polymerizations of poly(lactic acid) (PLA) during reactive extrusion process were investigated. In the presence of benzoyl peroxide as initiator and in the certain concentrations, effects of monomer type and concentration, extruder speed, and reaction temperature of reactive extrusion on the polymer reactions for the grafting percentage were studied.In this respect, radical melt graft polymerizations of PLA with two amide monomers of acrylamide (AM) and methacrylamide (MAM) were investigated, respectively. The results of Fourier transform spectroscopy (FTIR) analysis, elemental analysis, titration and dyeing tests confirmed that AM and MAM monomers were successfully grafted onto PLA. The optimum values ??for maximum percentage of graft extrusion reaction were: 12 mpm initiator of benzoyl peroxide, 450 mpm of AM and MAM, reaction temperature of 200° C and extrusion speed of 250 rpm. The structure of the monomer also affected the grafting percentage. From this molten radical melt grafted modified PLA polymers, fibers were melt spun. After exposure to chlorine bleach, the grafted modi?ed poly(lacti acid) fibers exhibited good antibacterial properties against Escherichia coli and Staphylococcus aureus . Also, optimal conditions of chlorinated bleach were determined to minimize its detrimental effects on the modified grafted antimicrobial PLA fibers. The optimum condition for chlorinated bleach was founded to be 0.1% active chlorine content, pH=10 and temperature of about 50°C, respectively.