In this paper, we have designed the digital filter based on rectangular Window function using ANN. Firstly we have designed the 10th order digital filter based on rectangular Window function then calculate the coefficient of designed filter.We have normalized the frequency and designed filter at frequency ranges 0.03 to 0.99 Hz. Then we calculated the coefficients of filter at these different frequencies. Some data group of coefficients is used to train the neural network, designed using generalized regression algorithm and rest data are used to test the input to neural network. The output corresponding to test input is approximate equal to frequency corresponding to calculated coefficients using FDA tool. The optimization of this neural network model has been done using generalized regression algorithm.