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In this study, we examined the species composition of neophyte communities of Robinia pseudoacacia and Acer negundo and compared the site conditions of the urban environment of two cities—Riga and Kaunas. Eighty-five plots of A. negundo and R. pseudoacacia communities were selected. Within each plot, all of the vascular plant species were recorded, and their abundance was estimated in 2014. Composite soil samples of the 0–10 cm mineral topsoil were collected for the estimation of the soil chemical properties at nine systematically distributed points in each sample plot. The soil pH KCL , exchangeable bases, total nitrogen, total organic matter, C/N ratio, and concentrations of the elements (P, K, Ca, Mg, Fe, Mn, Zn, Cu, Na, Pb, Cd, and Ni) were estimated. Canonical correspondence analysis was used to analyse the vegetation data. An indicator species analysis was carried out. The relationship between the soil chemical parameters was assessed by principal component analysis, and the results showed that structure and composition of the plant communities of A. negundo and R. pseudoacacia differed. The number of species was lower and the herb layer was more developed in R. pseudoacacia communities, whereas the structure of communities differed between Riga and Kaunas. The cover of the shrub layer was more developed in Riga. The number of species in A. negundo communities was similar, whereas the number of species in R. pseudoacacia communities was lower in Kaunas. Alien species were more frequent in Riga. Neophyte communities in Kaunas were more homogenous. The soil in communities in Riga had more carbon, was richer in nutrients and more acidic than in Kaunas. R. pseudoacacia grew in more fertile soils than A. negundo communities. The differences between the neophyte communities in Riga and Kaunas were caused by differing geological parameters, soil development and urbanization effects. [ABSTRACT FROM AUTHOR]