This experiment is conducted to show the work of FIR Low-pass Filter by Fast Fourier transform method for solving the problems of Windows method contract exceeds the specified frequency requirements.? The filter is tested on an input signal x (n) consisting of a sum of sinusoidal components at frequencies 440 880,,1000 2000, Hz. By setting the length of the design Windows method that M = 256 which allows and the Fast Fourier transform to. Be N = 512 samples. To get under low frequency through the frequency 600 Hz. Appropriate to the needs of the experiment.