To study possible modification of acrylic fiber, Cashmilon SF was treated with hexamethylene-diamine(HMDA) in toluene at elevated temperature. Physico-chemical properties of treated fiber were tested by dyeing with benzyl scarlet BS and by measuring tensile strength of the fiber. Following results were obtained from this experiment. 1) HMDA and fiber were condensed at above $120^{circ}C$. 2) Treated samples could be dyed with acidic dyes. 3) Treatment with HMDA decreased tensile strength of the fiber. This study therefore suggests that HMDA can be used to modify the properties of the fiber.