In recent years, one of the widely used techniques to improve the appereance of garments is screen printing. Curing of printed fabrics are achieved at high temperatures as 130-200 degrees C in this process. At these conditions, an important colour difference may occur between fabrics which are printed and not printed. In this study, the relationship between yellowing which occurs during the thermofixation of cotton fibres and pretreatments of the fibres were investigated in screen printing conditions. For this, different pretreatments were carried out and optimum recipe was investigated. Effect of pH to discolouration after thermofixation and hence, the way of achieving suitable pH levels are determined. Hydrophilicity, whitness (Stensby), yellowness (ASTM D 1925) values and L*, a*, b* coordinates of the samples were evaluated.