ENThe purpose of this paper is to compare usage results of the European Customer Satisfaction Index (ECSI) model for modelling customer satisfaction within supermarkets in Poland and Lithuania. Both countries became members of European Union and the common market relatively recently. This fact probably had an impact on changing consumer behaviour. Similarities and differences between these markets can be tested with ECSI model. This model was validated across a number of European countries and many industries. Its use can be interesting for newly joining European Union countries whose markets and consumer behaviours differ from the countries of the “old Union”. Lithuanian research was performed by Pilelienė and Grigaliūnaitė (2013). We adopted scales and variables used by them and ran parallel research in southern Poland. The research results showed considerable similarities. Both studies were not able to confirm the significant impact of customer expectations on perceived quality and perceived value. There was also no relationship between potential complaints and customer loyalty. In our study, we showed a greater impact of perceived quality on satisfaction and a smaller impact of perceived value. In the Lithuanian results, the perceived value had a greater impact on customer satisfaction. Keywords: european customers’ behaviour, European Customer Satisfaction Index (ECSI ) model, European Union markets, structural equation modelling (SEM), supermarkets.