Two different non‐Debye dielectric spectra are observed in different low‐frequency regimes in a polydomain relaxor ferroelectric single crystal, SrTi18O3, below its transition temperature,Tc≈ 23 K. Atf< 1 kHz the response is due to irreversible creeplike wall motion, &khgr;′ ∝ &khgr;″ ∝ &ohgr;−&bgr;with &bgr; ≈ 0.1 while polydispersive reversible wall segment relaxation with pink noise character is encountered at higher frequencies,f> 1 kHz. The crossover between both kinds of dielectric response is attributed to a dynamical phase transition [Nattermann et al., 2001]. © 2003 American Institute of Physics