Genome size variation is of fundamental biological importance and has been a longstanding puzzle in evolutionary biology. In the present study, the genome size of 61 accessions corresponding to 11 genera and 50 species of Vitaceae and Leeaceae is determined using flow cytometry. Phylogenetically based statistical analyses were used to infer ancestral character reconstructions of nuclear DNA contents. The DNA 1C-values of 38 species are reported for the first time, with the largest genome (Cyphostemma humile (N. E. Br.) Desc. ex Wild & R. B. Drumm, 1C=3.25pg) roughly 10.48-fold larger than the smallest (Vitis vulpina L., 1C=0.31pg). The large genomes are restricted to the tribe Cayratieae, and most other extant species in the family possess relatively small genomes. Ancestral genome size reconstruction revealed that the most recent common ancestor for the family had a relatively small genome (1C=0.85pg). Genome evolution in Vitaceae has been characterized by a trend towards genome size reduction, with just one episode of apparent DNA accumulation in the Cayratieae lineage. Such contrasting patterns of genome size evolution probably resulted from transposable elements and chromosome rearrangements, while neopolyploidization seems to contribute to recent genome increase in some species at the tips in the family tree.