To obtain a fine denier PET fiber split from a side-by-side type conjugate fiber which consists of regular PET and alkali soluble copolyester (CoPET), the conjugate fiber was treated in a aqueous sodium hydroxide solution and its hydrolysis behavior was investigated. The hydrolysis of the conjugate fiber progressed in two stages; the CoPET component hydrolyzed initially and the regular PET component hydrolyzed gradually later. As treatment temperature and concentration of sodium hydroxide increased, rate of hydrolysis of the conjugate fiber increased. When hydrolysis was rapid, however, the conjugate fiber did not show two stage hydrolysis behavior because of the simultaneous hydrolysis of PET and CoPET components. By means of SEM and DSC analysis, it was confirmed that the complete splitting of the conjugate fiber could be achieved at the weight loss which was 5~10％ higher than the CoPET content in the fiber, When a fabric which consisted of regular PET fiber in warp and PET/CoPET conjugate fiber in weft was hydrolyzed in the same conditions as above, wettability and handle values of the fabric greatly increased with the increase in the weight loss of the fabric. Tensile strength of the fabric decreased slowly until the weight loss reached the CoPET content in the fabric, and after that point it decreased significantly with increase in weight loss