Ageing phenomena on dielectric constant and dielectric losses of pure and compositionally modified PbZrO3 by Ba2+ ions are presented both in antiferrolelectric and ferroelectric phases. It is shown that the room temperature stable antiferroelectric phase of the samples gets inhibited on cooling after a heating cycle. The phase recovers from metastable ferroelectric phase on long-term ageing at room temperature. The antiferroelectric (Pb1-x Ba (x) )ZrO3 system having higher internal stress has a great driving force for higher ageing rate. It is also shown that the ageing process is more pronounced if the sample is thermally activated and the room temperature ageing leads to linear dependence of dielectric constant and dielectric losses upon logarithmic of time. It is proposed that the decrease in dielectric constant with time is due to the motion of domain walls coming from the domain nucleation as well as the stress relaxation.