Abstract <p>The aim of this study was to assess the intensity of organic matter transformation in urban soils affected by motor transport. Comprehensive seasonal terrain studies were performed in 2023‒2024 in the southwest of Moscow (Russian Federation). Chemical properties and biological activity of soils were studied. Two indicators—cellulolytic activity and biological oxygen consumption—were used to assess the biological destruction of organic matter. The pH value of roadside soils was 7.8 ± 0.6, the electrical conductivity was 185&#xa0;± 98 μS/cm, and the organic carbon content was 4.8 ± 2.1%, which corresponded to published data on urban soils in Moscow. It was revealed that the biological activity of soils of roadside lawns and median strips was characterized by significant dispersion of values: from 38 to 87%, depending on the season. The rates of cellulolytic activity in roadside soils were the highest in the summer-autumn and spring observation periods: 11.9 ± 7.6 and 12.0 ± 3.0 mg mg/g of organic matter per day (mg/(g day)), respectively. During the cold season, it was several times smaller: 4.1 ± 3.1 mg/(g day). In spring, the biological activity of urbo-soddy-podzolic soils (Retisols (Technic)) in central parts of large urban greenery areas was six times lower than in roadside soils. In other seasons, no reliable dependences were found between the studied indicators and the traffic intensity. The leading factors, determining the intensity of organic matter biological decomposition in urban soils under the impact of motor transport, include specific soil formation in constructozems (Technosols), urban microclimate, and differences in geochemical features of roadside soils due to chemicals applied during road maintenance works.</p>