Thermal modeling and optimal design of a gasket plate heat exchanger are presented in this paper. The method is applied to estimate the heat exchanger pressure drop and the effectiveness of chevron plates. Corrugation angle, amplitude, and wavelength of chevron corrugation, plate width, plate length, and the number of plates are considered as six design parameters. The Fast and Elitist Non†Dominated Sorting Genetic Algorithm (NSGA†II) is applied to obtain the maximum effectiveness and the minimum total annual cost (sum of investment and operation costs) as two objective functions. The results of optimal designs are a set of multiple optimum solutions called" Pareto optimal solutions". The sensitivity analysis of change in optimum effectiveness and total annual cost with change in design parameters of the gasket plate heat exchanger is also performed and the results are reported. It is also investigated that effectiveness is proportional to the nondimensional parameter of corrugation amplitude to wavelength in the optimum situation.