  In this paper, we analyse spectral properties of Seidel matrix (denoted by
$S$) of connected threshold graphs. We compute the characteristic polynomial
and determinant of Seidel matrix of threshold graphs. We derive formulas for
the multiplicity of the eigenvalues $\pm 1$ of $S$. Further we determine
threshold graphs with at most 5 distinct Seidel eigenvalues. Finally we
construct families of Seidel cospectral threshold graphs.
