Dielectric and thermal expansion studies have been carried out in the relaxer ferroelectric system of PFN 1 - x -PZN x . These compositions show two distinct regions of thermal expansion behaviour from room temperature to 80 K. As the T c of the system increases, the lower expansion region extends. At higher values of x (>0.7), the pyrochlore phase appears, resulting in higher values of α. Addition of BaTiO 3 suppresses the pyrochlore phase and reduces the magnitude of α in the relaxer region. The width of the low expansion region is also reduced due to the lowering of T c in these compositions.