Abstract: This research investigate the way of using the polar decomposition of matrix in solving the least squares problem. By using this decomposition, researchers can solve the liner system. Also, this study included the way of obtaining inverse of a non-singular matrix and determinant of a matrix by this decomposition. Finally, the problem of least squares solved by normal equations and Pseudo-inverse matrix by using the polar decomposition. With solving some example, researchers show that the accuracy of this method.