In this work, Differential Evolutionary Algorithm (DEA), a novel and commonly used optimization algorithm in engineering problems, is applied for the design optimization of a low pass filter with exponential transmission lines. Basically the principle of DEA is similar to genetic algorithms techniques, however compare to meta-heuristic algorithms it has a much simpler algorithm structure and higher stability compare to its counterpart algorithms. For design optimization of low pass filter with exponential transmission lines, each of the transmission lines width and variation with its length are taken as an optimization variable for DEA. Firstly the unit microstrip transmission line model is chosen. After that, the optimal value of widths and lengths are obtained via DEA. The cost function of the DEA is based on the calculation of scattering parameters of candidate's solutions crossed the requested frequency bandwidth.