The virus types in tobacco seedling samples of floating system before and after transplanting were detected with double- and triple-antibody sandwich enzyme-linked immunosorbent assay (ELISA) . The test results of over 1400 tobacco seedling samples collected before transplanting showed that tobacco mosaic virus (TMV) was the major virus infecting seedlings in floating system in Yunnan Province, and accounted for a proportion of over 95% ; while the proportion of cucumber mosaic virus (CMV) and potyviruses (including potato virus Y and tobacco etch virus ) was less than 5% . The TMV positive percentage of seedlings in an infected floating system was relatively higher (15% - 80%) ; in the seedbed under good management, the seedlings showed lower TMV positive percentage (0 - < 0.5%) . The test results of 697 leaf samples with the symptom of tobacco mosaic collected at rosette stage in seriously infected field (mosaic disease incidence was more than 20%) indicated that TMV remained the major virus, with a detected rate of 48.1% to 100%, while that of CMV and Potyviruses was 0 -12.2%. Therefore, the integrated control against virus during floating seedbed stage and early stage after transplanting in field should be focused on TMV.