In this paper, an optimization procedure is performed by response surface methodology to optimize the position and size of the partition inside a single slope solar still. The partition is installed separately at bottom surface and glass cover of the still to improve the performance. The optimization procedure is performed to determine the maximum Nusselt number as a response. Two-dimensional steady equations with laminar assumption have been solved using a finite volume approach. Analysis is performed for a fixed value of Rayleigh number. Beside this, a sensitivity analysis is performed to calculate the sensitivity of the response (Nusselt number) to the position and size of the partition. Results show that the real optimized parameters for the maximum normalized Nusselt number of bottom installed partition are X' = 0.23 and Y' = 0.18. These parameters for the the maximum normalized Nusselt number of top installed partition are X' = 0.53 and Y' = 0.56162. Also, the installation of partition leads to an increase in vortices number with smaller sizes. Smaller vortices provide sufficient pathways to heat exchange and increase the still efficiency. (C) 2016 Elsevier B.V. All rights reserved.