Urban traffic is the largest source of atmospheric pollution that constitutes about 90 - 95% of the total volume of pollutants that are discharged into the atmosphere. The degree of harmfulness of exhaust emissions decreases according to the following sequence: SO2 > NO > CO > CO2, thus the need for the research of SO2 influence on the biological diversity arises. Some authors consider that the sulphur content in the leaves can be used as an indicator of sulphur dioxide absorption. Sulphur compounds accumulate more in the leaves of old trees than in young ones because of long-term exposure to noxious pollution. Some plant species appear to be more susceptible than others are, although all plants are sensitive to SO2. The present study is designed to evaluate the cumulative amount of sulphur in the leaves of three tree species in five locations Chisinau Urban Ecosystem. Thus, three plant species (Tilia cordata, Acer platanoides, Pinus nigra) were analysed on the sulphur content in the leaves. For all three analysed species, the sulphur content in leaves increases according to the relation: st. Calea Ieșilor > st. Botanical Garden > st. Bd. Moscova > st. CET 1.