Abstract: Experiments on the alkaly deweighting of easy cationic dyeable polyester(ECDP) were introduced.Investigations on the relationship between the deweighting ratio and the concentration of NaOH,the treating temperature and time,as well as the liquor ratio were carried out.Influences of molecule weight of ECDP fiber,yarn strength,the percentage of dye exhaustion to the deweighting ratio were indicated.In the reduction of weight with base process,the deweighting ratio of ECDP fiber was higher than FDY fiber with the same concentration of NaOH,the treating temperature and time,as well as the liquor ratio.As the deweighting ratio increase,the fiber yarn strength has been lost in linear function.ECDP fibers compare to FDY fibers in the same deweighting ratio,yarn strength of it decrease quickly; ECDP fiber hydrolysis rate is quicker than common polyester fiber;The molecule weight of ECDP fiber is decrease quickly.The percentage of dye exhaustion is lower when the deweighting ratio increase.