Street dusts are suspended particle matters in the air from different natural and anthropogenic sources that may fall out because of their size and density. Forty nine street dust samples were collected from some main streets of eastern and southern parts of Tehran. One other sample was also collected from Iran University of Science and Technology central campus for comparisons during summer under dry and stable weather conditions. The concentrations of Cu, Cr, Pb, Ni, Cd, Zn, Fe, Mn and Li in samples were determined. Correlation, cluster and principal component analyses were used to identify probable sources of metals in street dust. In addition possible effects of human activities on the concentrations of heavy metals were evaluated using enrichment factors (EFs). The results show high concentrations of Cd, Pb, Cu, Cr, Ni, Zn and Fe in Tehran street dust. Maximum concentrations of Pb, Cu, Cr, Ni, Zn and Fe were observed in dust samples along Baghery highway which is one of the highly traffic loaded highways of Tehran. The results revealed that contaminants can might be originated from anthropogenic sources such traffic and fuel combustion related activities, metallic surfaces corrosion, road pavements and building materials. EF values for Cu, Cd, Pb and Zn demonstrated that they are highly enriched in dust. Ecological risk assessments and risk indexes (RI) were performed using Hakanson’s method. The highest ecological risk is contributed to Baghery highway too. Mean EF value for metals was 126. The highest EF value was the one for Cd that is about 1600. Regarding the results of RI and EF, the pollution severity of Cd is more than other metals so it might have more adverse effects on health and urban environment of Tehran. Ecological risk of metals was also very high for all dust samples.