The aim of this study was to determine the influence of human pressure and spatial structure of landscape on the occurrence of populations of small mammals in the environment of a large urban agglomeration. The investigations were carried out in Warsaw, Poland in 17 locations. The study sites were located on both sides of the Vistula River, of different landscape spatial structure, in various distances from the city center, and were subject to different degrees of human pressure. Part of the city located on the left bank of the Vistula River is more strongly transformed by man than the part located on the right bank of the river. A total of 933 specimens of 8 species of small mammals were caught using the live-trapping method (Catch-Mark-Release). The richest species composition was found at the city borders and in rural areas. On the left side of Vistula, the species diversity was lower than on the right side, showing significant negative correlation with the human pressure degree. Such pattern was not confirmed on the right side of the river. The only species to occur in all sites on the left side of Vistula was the striped field mouse (Apodemus agrarius). On the right side of Vistula, the striped field mouse was accompanied by the yellow-necked mouse (Apodemus flavicollis) in all research sites. The results indicate that the degree of human pressure and spatial isolation are crucial for composition of small mammal community. Less advanced urbanization processes in areas on the right bank of Vistula, as compared to districts on the left side, provide better contact between local populations of small mammals, and offer better living conditions to a large number of species, even in areas located in the center of the city