A comparison of the actual vascular flora of the Tiber in Rome with a similar floristic survey of the 1970s was carried out. Changes in species richness, floristic composition and structure occurred in the last 30 years were described and dynamics of abundance of each species was estimated. The total number of species decreased from 604 in 1975–1981 to 501 till date. The composition of the Tiber flora has partially changed. There has been a decrease in therophytes on the riverbed and an increase in hydrophytes especially eutrophic ones. Most of Mediterranean species and those associated with undisturbed land have been replaced by widely distributed, ruderal and alien species, as human influences have increased. The floristic variations were used as indicator to evaluate the effect of human impact on the development of site and to describe the main changes in river management and bank use occurred locally over the last decades.