Electrical demulsification is one of ways to separate two phases of liquids, based on the processes of electrodeformation and electrocoalescence. However, the interfacial tension of a liquid pair turns out to be not constant over time. It has been experimentally ascertained that the interfacial tension reduces for a number of pairs of liquids. Moreover, there are cases of an actual decrease in the interfacial tension and those of fictitious ones. The interfacial tension change throughout various times was observed for two pairs of liquids: distilled water / olive oil and distilled water / polydimethylsiloxane-50.