Let $Γ=(G,σ)$ be a signed graph and $A(G,σ)$ be its adjacency matrix. Denote by $gr(G)$ the girth of $G$, which is the length of the shortest cycle in $G$. Let $r(G,σ)$ be the rank of $(G,σ)$. In this paper, we will prove that $r(G,σ)\geq gr(G)-2$ for a signed graph $(G,σ)$. Moreover, we characterize all extremal graphs which satisfy the equalities $r(G,σ)=gr(G)-2$ and $r(G,σ)=gr(G)$.