In this paper we presented our experimental results of in situ TEM observations of ferroelectric phase transitions in BaBa2NaNb5O15 (Tc =550℃) and LiTaO3 (TC = 660℃). At room temperature the domain patterns are of the scale 0.2-1 μm. Increasing the temperature to near Tc, the micro-domains forming quasi-regular arrays of the scale about several hundreds of angstroms have been observed and interpreted according to a model slightly modified from that of Селок. A strong susceptibility to radiation damage is found in LiTaO3 near phase transition temperature which may be connected with soft modes of phase transitions.