WWI had a significant impact on European citizens, including social, economic and political changes. In 1918 Poland regained its independence after 123 years of partitions. After the liberation, the citizens struggled with poverty, unemployment and post-war destruction. The aim of the study is to investigate the changes in marriage patterns, including changes in the age of entering into matrimony and the criterion of the partner selection before and after WWI. For this purpose, registration cards of the Poznań inhabitants for the years 1870-1931 were used. The research used the following information: date and place of birth of the spouses, dates of marriage, marital status, religion and social status of the partners. The age at marriage was calculated for men and women due to their socio-cultural factors. Coefficients of correlation between ages at marriage of partners by their socio-economic status were calculated. A correlation was shown between the age of partners and between their territorial mobility. The analysis of Cox proportional hazard showed a significant influence of marital status, religion and territorial mobility on partner selection. After 1918, people married later than before the war. The economic disparities between city and countryside, the Spanish flu at the end of WWI, the economic crisis in the 1920s as well as social and religious disproportions in the country influenced the partner selection and age at marriage.