Yellow leaf curl disease was observed in tomato (Solanum lycopersicum) plants in Yunnan Province, China. Analysis of the full-length viral DNA isolated from an infected tomato plant indicated that the viral genome contained 2759 nucleotides (nt) and had the typical genome structure of begomoviruses. Further analysis of the viral sequence showed that it shared the highest nt sequence identity (86.0%) with Tomato yellow leaf curl Vietnam virus (TYLCVNV) previously identified in Vietnam. The virus is therefore a new Begomovirus species for which the name Tomato yellow leaf curl Yunnan virus (TYLCYnV) has been proposed. The betasatellite was also obtained and showed the highest nt sequence identity (70.1%) with Tomato yellow leaf curl China betasatellite (TYLCCNB).