  We study the action of the $SL(2;R)$ group on the noncommutative DBI
Lagrangian. The symmetry conditions of this theory under the above group will
be obtained. These conditions determine the extra U(1) gauge field. By
introducing some consistent relations we observe that the noncommutative (or
ordinary) DBI Lagrangian and its $SL(2;R)$ dual theory are dual of each other.
Therefore, we find some $SL(2;R)$ invariant equations. In this case the
noncommutativity parameter, its $T$-dual and its $SL(2;R)$ dual versions are
expressed in terms of each other. Furthermore, we show that on the effective
variables, $T$-duality and $SL(2;R)$ duality do not commute. We also study the
effects of the $SL(2;R)$ group on the noncommutative Chern-Simons action.
