Weight reductio i a finishing proce with the aim of improving some propertie of polyester fabric through hydrolysis, with the hel of aqueou alkaline such a sodium hydroxide. The amount of weight reductio with sodium hydroxide depend o processing parameter such a concentratio of sodium hydroxide, treatment time and bath temperature. Thi work i aimed at modeling of weight reductio of PET fabric a a functio of NaOH concentration, temperature and time and cost minimization. The experiment were designed with a full factorial approach. Three level were assigned for the three above mentioned factors. The data were gathered and their variatio were analyzed a to reveal the degree of significance of each factor. Next a response surface regressio model wa established with the significant factors. After the evaluatio of the model, we used Box-Cox method for further modification. Finally by determining the cost function, the proce variable leading to minimum cost for a the predetermined weight reductio percentage, were obtained