  Let $G_w$ be a weighted graph. The \textit{inertia} of $G_w$ is the triple
$In(G_w)=\big(i_+(G_w),i_-(G_w), $ $ i_0(G_w)\big)$, where
$i_+(G_w),i_-(G_w),i_0(G_w)$ are the number of the positive, negative and zero
eigenvalues of the adjacency matrix $A(G_w)$ of $G_w$ including their
multiplicities, respectively. $i_+(G_w)$, $i_-(G_w)$ is called the
\textit{positive, negative index of inertia} of $G_w$, respectively. In this
paper we present a lower bound for the positive, negative index of weighted
unicyclic graphs of order $n$ with fixed girth and characterize all weighted
unicyclic graphs attaining this lower bound. Moreover, we characterize the
weighted unicyclic graphs of order $n$ with two positive, two negative and at
least $n-6$ zero eigenvalues, respectively.
