Abstract: A new method based on third-order tensor decomposition is proposed to solve the problem of target number estimation in bistatic multiple-input multiple-output ( MIMO) radar. First, the matched filter output is transformed to a third-order tensor. Then, the eigenvalues are calculated from three dimensions of this tensor, and the global eigenvalue is obtained by an iterative method. At last, the target number can be estimated using the global eigenvalue. Compared with the traditional matrix decomposition approach, the proposed method takes the multi-dimensional structure of the echo data into account, which results in better estimation accuracy of the eigenvalues. Consequently, the correct estimate probability of the target number is improved. The effectiveness and superiority of the proposed method is demonstrated by simulation results.