This paper proposes a new FIR(finite impulse response)filter under a least squares criterion using a forgetting factor.The proposed FIR filter does not require information of the noise covariances as well as the initial state,and has some inherent properties such as time-invariance,unbiasedness and deadbeat.The proposed FIR filter is represented in a batch form and then a recursive form as an alternative form.From discussions about the choice of a forgetting factor and a window length,it is shown that they can be considered as useful parameters to make the estimation performance of the proposed FIR filter as good as possible.It is shown that the proposed FIR filter can outperform the existing FIR filter with incorrect noise covariances via computer simulations.Finally,as a useful application,an image sequence stabilization problem is considered.Through this application,the FIR filtering based approach is shown to be superior to the Kalman filtering based approach. This paper proposes a new FIR (finite impulse response) filter under a least squares criterion using a forgetting factor. The proposed FIR filter does not require information of the noise covariances as well as the initial state, and has some inherent properties such as time- invariance, unbiasedness and deadbeat. The proposed FIR filter is represented in a batch form and then a recursive form as an alternative form. Flash discussions about the choice of a forgetting factor and a window length, it is shown that they can be considered useful parameters to make the estimation performance of the proposed FIR filter as good as possible. It is shown that the proposed FIR filter can outperform the existing FIR filter with incorrect noise covariances via computer simulations. Finaally, as a useful application, an image sequence stabilization problem is considered.Through this application, the FIR filtering based approach is shown to be superior to the Kalman filtering based approach.