The purpose of this work was to optimize the formulation of a prebiotic dairy dessert with low fat content (<0.1 g/100 g) using a mixture of short- and long-chain inulin. Response surface methodology was applied to obtain the experimental design and data analysis. Nineteen formulations of dairy dessert were prepared, varying inulin concentration (3 to 9 g/100 g), sucrose concentration (4 to 16 g/100 g), and lemon flavor concentration (25 to 225 mg/kg). Sample acceptability evaluated by 100 consumers varied mainly in terms of inulin and sucrose concentrations and, to a lesser extent, of lemon flavor content. An interaction effect among inulin and sucrose concentration was also found. According to the model obtained, the formulation with 5.5 g/100 g inulin, 10 g/100 g sucrose and 60 mg/kg of lemon flavor was selected. Finally, this sample was compared sensorially with the regular fat content (2.8 g/100 g) sample previously optimized in terms of lemon flavor (146 mg/kg) and sucrose (11.4 g/100 g). No significant difference in acceptability was found between them but the low-fat sample with inulin possessed stronger lemon flavor and greater thickness and creaminess.