  Let $n$, $k$ and $t$ be integers with $1\leq t< k \leq n$. The
\emph{generalized Kneser graph} $K(n,k,t)$ is a graph whose vertices are the
$k$-subsets of a fixed $n$-set, where two $k$-subsets $A$ and $B$ are adjacent
if $|A\cap B|<t$. The graph $K(n,k,1)$ is the well-known \emph{Kneser graph}.
In 2014, Harvey and Wood determined the exact treewidth of the Kneser graphs
for large $n$ with respect to $k$. In this paper, we give the exact treewidth
of the generalized Kneser graphs for $t\geq2$ and large $n$ with respect to $k$
and $t$. In the special case when $t=k-1$, the graph $K(n,k,k-1)$ usually
denoted by $\overline{J(n,k)}$ which is the complement of the Johnson graph
$J(n,k)$. We give a more precise result for the exact value of the treewidth of
$\overline{J(n,k)}$ for any $n$ and $k$.
