The objective of this study was to model and optimize the mass transfer behavior during microwave osmotic dehydration of apple cylinders under continuous-flow spray mode processing conditions. Data needed for the model development and optimization were obtained using a central composite rotatable experimental design involving sucrose concentration (33.3–66.8°B), temperature (33.3–66.8 °C), flow rate (2,120–3,480 ml/min), and contact times (5–55 min); and the response variables were moisture loss, solids gain, and weight loss. Mass transfer kinetics was evaluated based on the empirical Azuara model and the conventional diffusion model. Diffusivities of both moisture loss (Dm) and solids gain (Ds) obtained from the diffusion model were related to sucrose concentration, temperature, and flow rate. Optimization was evaluated using a desirability function model which could be used with several imposed constraints. The optimum conditions obtained depended on the imposed constraints. A set of constraints involving maximizing moisture loss and weight reduction while keeping the solids gain below 3.5% gave the following optimal conditions: a 30-min osmotic treatment at 65°B, 60 °C, and 2,800 ml/min flow rate yielding a moisture loss of 40.9%, weight reduction of 37.7%, with a solids gain of 3.32%.