The differential response of two papaya cvs. ‘Kaek Dum’ and ‘Red Maradol’ to 1-methylcyclopropene (1-MCP) applied at 100 nl l-1 at <10% yellow peel color was evaluated based on physiological changes and rate of fruit softening in relation to the activities of cell wall degrading enzymes and solubilization of cell wall polysaccharides. Ethylene production, respiration rate, softening, activities of cell wall degrading enzymes and the solubilization of cell wall polysaccharides were lower in ‘Red Maradol’ compared to ‘Kaek Dum’. In both cultivars, 1-MCP suppressed ethylene production and respiration rate, delayed the onset of the climacteric and retarded the softening process. The delay in the softening of 1-MCP-treated fruit was greater in ‘Red Maradol’ compared with ‘Kaek Dum’ coincident with the low activities of polygalacturonase (PG) and β-galactosidase. Consequently, changes in the pectic, hemicellulosic and cellulosic fractions were reduced. These results account for the slower rate of softening of ‘Red Maradol’ than ‘Kaek Dum’ papaya.