Introduction. Mucopolysaccharidosis IVA (Morquio A) is caused by a deficiency of N-acetylgalactosamine-6-sulphate-sulphatase, a lysosomal enzyme required for the stepwise degradation of keratan-sulfate and chondroitin-6-sulfate. A deficiency in this enzyme results in an accumulation of glycosaminoglycans in several tissues. Currently, no effective therapies exist and only supportive measures are used to treat some manifestations of the disease. An ideal therapy is one that can be administrated early in life, has low mortality, and leads to long-term expression of the enzyme. Gene therapy emerges as a potential alternative to correct the genetic defect in MPS IVA. Objective. Adenoassociated virus-derived expression vectors (AAV) were constructed to correct in vitro the enzyme deficiency in mucopolysaccharidosis IVA. Materials and methods. Adenoasociated virus-derived vectors containing the human GALNS gene and driven by the citomegalivirus immedited-early promoter were constructed using a free-adenoviral protocol. HEK293 cells and human skin Morquio A fibroblasts were transfected with the recombinat vectors. Enzyme activity was measured in cells 24 and 48 hours post-transfection. Results. Free-adenovirus recombinant AAV vectors were obtained with titres up to 2.08x1010 capsids/mL. HEK293 cells and Morquio A fibroblasts transfected with vectors showed GALNS activity up to 3.05 nmoles/mg/h 48 hours post-transfection. Conclusion. The AAV mediated the in vitro expression of GALNS enzyme in the transfected cells. These results are the first step towards a gene therapy alternative to Morquio A disease using adenoassociated virus-derived vectors.