The present study aims to investigate exergy efficiency of a Flat-plate solar collector containing Al2O3-water nanofluid as base fluid. The effect of various parameters like mass flow rate of fluid, nanoparticle volume concentration, collector inlet fluid temperature, solar radiation, and ambient temperature on the collector exergy efficiency is investigated. Also, the procedure to determine optimum values of nanoparticle volume concentration, mass flow rate of fluid, and collector inlet fluid temperature for maximum exergy efficiency delivery has been developed by means of interior-point method for constrained optimization under the given conditions. According to the results, each of these parameters can differently affect the collector exergy by changing the value of the other parameters. The optimization results indicate that under the actual constraints, in both pure water and nanofluid cases the optimized exergy efficiency is increased with increasing solar radiation value. By suspending Al2O3 nanoparticles in the base fluid (water) the maximum collector exergy efficiency is increased about 1% and also the corresponding optimum values of mass flow rate of fluid and collector inlet fluid temperature are decreased about 68% and 2%, respectively. (C) 2015 Elsevier B.V. All rights reserved.