The main aim in the synthesis of acid- labile cross linker is to achieve the desired pH-responsive behaviour, i.e. rapid cleavage in slightly acidic pH such as those present in intracellular vesicles of the cells (pH4.5-6.8), and stability for long time in the blood, i.e. pH 7.4. The acetals synthesized from p-substituted benzaldehydes have been shown by the previous studies [15,30] to be particularly well suited to this purpose as their acidlabile behaviour can be tailored by introducing different substituent's at the para-position of the benzaldehyde. Thus, the use of the cross linkers containing psubstituted benzaldehyde acetals as an intrinsic acidresponsive element provides an easy and versatile way to incorporate and engineer the acid-cleavability to the polymeric colloidal systems for the site-specific drug release.