Abstract: An optimized structured (OS) preconditioner for a class of complex symmetric linear systems is proposed. The OS-preconditioner results in a fast Krylov subspace solver, which is robust with respect to the mesh-size. The computational complexity of OS-preconditioner is analyzed and it is shown that all eigenvalues of the corresponding preconditioned matrix are positive real and distributed on \left\frac12+\frac\varepsilon2 \sqrt1+\varepsilon^2, 1\right. Numerical experiments confirming the theoretical derivations are presented to verify the effectiveness and stability of the OS-preconditioner.