Many active ingredients tend to cause undesirable effects when administered orally, as it is the case of anti-inflammatory drugs that produce irritation in the stomach. An alternative to this problem is the microencapsulation of these substances in a suitable matrix. Chitosan because of its excellent properties: non-toxic, biocompatible, biodegradable and anti-ulcer activity is a polymer widely used for this purpose. In the present study chitosan (QUI) microparticles were prepared by a simple coacervation procedure followed by cross-linkig with sodium tripolyphosphate (TPP). The microparticles were loaded with dexamethasone and then were coated with a pH-sensitive interpolymer complex based on poly (acrylic acid) (PAA) and poly(ethylene glycol) (PEG) of different molecular weights, to prevent its release and degradation in the stomach. The study of complex formation in water solution revealed that increasing molecular weight of PEG increases the stability of the formed complex. The particles were characterized by scanning electron microscopy (SEM). It was observed that particles had a smooth surface that became rough after being covered by the polymer mixture. The in vitro release study of dexamethasone encapsulated was carried out in simulated fluids, gastric (pH = 1.2) and intestinal (pH = 6.8). Dexamethasone release from the coated microparticles in simulated gastric fluid was significantly reduced as compared with the non-coated particles. The dexamethasone released was determined by UV-Visible spectroscopy at 242 nm.