In this paper a sufficient condition for determining controllability and observability of linear symmetric interval systems is proposed, where the transformation matrix is obtained such that the transformed interval system matrix is diagonal. Then the symmetric interval system is said to be controllable if it is controllable in usual sense for each fixed value of uncertain parameters of the interval system. Similarly the symmetric interval system is said to be observable if it is observable in the usual sense for each fixed value of uncertain parameters of the given interval system. Numerical examples illustrate the procedure.