The effects of Ba2+ substitution on the dielectric properties and induced strain behaviour of the (Pb1-xBax) ZrO3 ceramics (0.05 less than or equal to x less than or equal to 0.3) have been investigated as a function of x. A new phase diagram of the (Pb1-xBax) ZrO3 system, indicating the field effect on the phase transition, is also presented. As the Ba2+ content increases, the Curie temperature decreases linearly, whereas maximum dielectric constant increases for up to 20 mol% Ba2+ addition, and then decreases with further Ba2+ addition. Based on the hysteresis loops, the temperature range of the ferroelectric phase as an intermediate phase between the antiferroelectric and paraelectric phases, increases with increasing electric field and Ba2+ content. The ferroelectric loops are induced at room temperature for the specimens containing above 10 mol % Ba2+ by applying an electric field up to similar to 25 kV cm(-1). However, for the 5 mol% Ba2+-substituted specimen, no ferroelectric loop is induced, even with applied fields up to 55 kV cm(-1). The phase transition due to electric field and Ba2+ addition is also confirmed by the measurement of the field-induced longitudinal strain.