Urban vacant lots (VLs) can harbour a large number of rare and endangered species.In the present study, we evaluated species composition and biodiversity of plant communities inhabiting VLs in the City of Mashhad, northeastern Iran. We used a line transect sampling method to sample 98 random VLs along different districts of the City. We classified VLs based on their species composition and environmental factors. Then, a significant difference in the community composition along with the dominant and indicator species of clusters was evaluated. Also, we compared species and phylogenetic diversities of clusters. We identified four clusters. The species composition of the four clusters was different. One cluster (i.e., D912) had more rangerestricted species than the other clusters. This cluster also had a higher species and phylogenetic diversity than the others. Two clusters had the lowest phylogenetic diversity in comparison with the others. Our results implied that income distribution in the city had indirect effects on plant communities of VLs. Vegetation of VLs in areas with higher average income was less damaged than that of the lower-income areas. Because of its most diverse and range-restricted plants, the D912 cluster should be managed to maintain the biodiversity in the city. Land use change to parks or urban agricultural lands is suggested for degraded and species-poor VLs.