The polarization switching in methylammonium chlorobismuthate, (CH3NH3)5Bi2Cl11, single crystal was investigated by optical observations of the domain structure and switching current registration. It is shown that defects introduced during crystal growth influence the polarization switching kinetics. For the analysis of switching current data the statistical Avrami model of phase transformation kinetics was employed. Direct observation of the domain structure enabled us to verify the assumptions of the Avrami model in the case of non-uniform (CH3NH3)5Bi2Cl11 crystals. It is found that application of this model to non-uniform crystals can yield physically unclear values of some fitting parameters; e.g. the effective domain growth dimension is not constant with respect to the electric field. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)