  Let $\Gamma=(K_{n},H^-)$ be a signed complete graph whose negative edges
induce a subgraph $H$. The index of $\Gamma$ is the largest eigenvalue of its
adjacency matrix. In this paper we study the index of $\Gamma$ when $H$ is a
unicyclic graph. We show that among all signed complete graphs of order $n>5$
whose negative edges induce a unicyclic graph of order $k$ and maximizes the
index, the negative edges induce a triangle with all remaining vertices being
pendant at the same vertex of the triangle.
