In this paper, we derive bounds for the complex eigenvalues of a nonsymmetric saddle point matrix with a symmetric positive semidefinite .2, 2/ block, that extend the corresponding previous bounds obtained by Bergamaschi. For the nonsymmetric saddle point problem, we propose a block diagonal preconditioner for the conjugate gradient method in a nonstandard inner product. Numerical experiments are also included to test the performance of the presented preconditioner.A large variety of applications and numerical solution methods of (1) or (2) have been comprehensively reviewed by Benzi, Golub, and Liesen [1]. Recently, the eigenvalue distribution of the nonsymmetric saddle point matrix A has been deeply studied. On one hand, eigenvalue bounds for A can be used to analyze the spectral properties of preconditioners such as symmetric indefinite preconditioners, inexact constraint preconditioners and primal-based penalty preconditioners for (1); see, for example, [3][4][5][6]. On the other hand, eigenvalue estimates for A can give theoretical basis for the CG method for (2) in a nonstandard inner product; see, for example, [3,[6][7][8]. This paper aims to provide further bounds for the complex eigenvalues of A that extend the corresponding ones in [4].An efficient implementation of the CG method for (2) has been established by Liesen and Parlett [7]. The authors pointed out that preconditioning should be studied in practical applications,(1) If Im( )=0, then minf% 1 , & 1 g 6 6 maxf% n , m g.