Abstract: of the causal agents of cruciferous vegetable mosaic diseases around Fuzhou, isolate No. 26 (the virus isolated from diseased plants of Brassica sp.) was an important one,its frequency being 26.4%.This virus was identified as a strain of TMV on the basis of antiserum reaction, and physical and other properties.The physical properties of this virus were similar to those of TMV, its thermal death point being 98-100℃, the aging period more than 778 days and the dilution end point 10-12-10-13.The virus was transmitted easily by sap inoculation and less easily by larvae of white flies(Pieris rapae Linn.) .It was not transmitted by false cabbage aphides (Rhopolosiphum pseudobrassicae Dav.) or by the seeds of diseased cruciferous plants. Soil mixed with flesh residues of diseased plants induced the infection of transplanted plants.Host range tests were made on 20 plant species or varieties belonging to 13 genera of 8 families. Of them, 14 plant species or varieties belonging to 9 genera of 6 families, including Cruciferae, Solanace-ae, Compositae, Chenopodiaceae, Amaranthaceae and Plantaginaceae were found to be susceptible.Antiserum reation between ordinary TMV antiserum and this virus antigen produced a clear precipitative band, and indicated that two vruscs are related. The particles of this virus were measured 300-400 nm. in Length and 18-19 nm. in diameter, With typical centval cores and spiroid structure of pvotein snbunits.