This thesis focuses on the development of an aerodynamic optimization algorithm for long range mini-UAV’s. This algorithm is applied to the design of the TU Delft mini- UAV that participated in the EMAV2009 outdoor endurance mission. The analysis of the low Reynolds number (< 2.5 · 105) aerodynamics on the wing is performed using a quasi-3D method which combines a vortex lattice method with viscous airfoil data. The optimization part of the program is accomplished by a sequential quadratic programming algorithm. RANS-CFD calculations and wind tunnel experiments were performed to validate the newly developed quasi-3D method. The final design for the mini-UAV has lift over drag ratio of 11.8 and a high capacity battery (8Ah) which give it a total range of 166 km