The olive tree (Olea europaea L.) has been cultivated around the Mediterranean basin since ancient times, ‘Arbequina’ being one of the most widely grown varieties. To improve the knowledge on ripening-related firmness changes in olive fruit, cell wall metabolism was studied in irrigated and rain-fed ‘Arbequina’ olives grown at ‘Les Garrigues’, a Protected Designation of Origin (PDO) in Catalonia (NE Spain) where harsh environmental conditions occur during fruit development. Fruit samples were picked periodically from September to January. Time-course dynamics of firmness loss during maturation were characterised by a first phase of rapid firmness loss followed by a second phase of moderate change. Compositional changes in cell walls and related enzyme activities were studied in fruit samples. Fruit firmness was significantly higher in rain-fed than in irrigated olives. Neutral sugar loss, an early event in ripening-related cell wall modifications, was lower in rain-fed samples, which, moreover, retained higher uronic acid amounts in the chelator-soluble fraction, thus resulting in attenuated firmness loss in these fruits.