The sum-connectivity index of a graph $G$ is defined as the sum of weights $1/\sqrt{d_u+d_v}$ over all edges $uv$ of $G$, where $d_u$ and $d_v$ are the degrees of the vertices $u$ and $v$ in graph $G$, respectively. In this paper, we give a sharp lower bound on the sum-connectivity index unicyclic graphs of order $n\ge 7$ and diameter $D(G)\ge 5$.
