Abstract: Th rough th ree years of invest igat ion s and studies by the Co llabo rat ive Group of 16m ain p rovinces ( region s)of tobacco p roduct ion in Ch ina, 62 infect iou s diseases of tobacco have been invest igated and iden t if ided. O f them, 11 diseases w ere f irst found in Ch ina, and 5 diseasesw ere f irst repo rted in the wo rld. They aretobacco stem speck (P hom a n icotianae Yu et Hua), tobacco bacterial leaf spo t X an thom onas camp estris pv. vesica toria (Do idge)Dye , tobacco bacterial b lack stem E rw in ia ca rotovola subsp, a trosep eitica (V an Hall) Dye , tobacco bacterial b lack ro t X an thom onas camp estris pv. camp estris (Pamm el)Dow son , and J apanese dodder (Cuscu ta jap on ica Cho rs), and all of them occu rred occasionally. O f the 62 diseases there are 15 seriou s ones, generally dist ribu t ing in 14～ 16 p rovinces ( region s) and cau sing seriou s lo sses in 1～ 14 p rovinces( region s). They are m ino r diseases o r do no t cau se seriou s lo sses in 2～ 9 p rovinces ( region s). A cco rding to catego ries of pathogen s, the 62 diseases m ay be divided in to: 30 cau sed by fungi, 8 by bacteria, 17 by viru ses, 2 by m ycop lasm a, 3 by nem atodes, and 2 by seed p lan t s.By the im comp lete stat ist ics in 1989～ 1991, the 5 diseases, tobacco mo saic ( including TMV, CMV and even PV Y), b row n spo t, b lank shank, bacterial Granville w ilt and nem atode roo t kno t, cau sed leaf lo ss to 0148 b illion kg and the ou tpu t value lo ss to 115 b illion yuan (RMB). These f igu res show the seriou sness of the tobacco diseases. F rom the viewpo in t of the developm en t h isto ry of phytopatho logy, tobacco diseases are a p resen t p ract ical and long- term po ten t ial th reat to the yield and quality of tobacco. Therefo re, it is a hard task to p ro tect the tobacco p roduct ion and to st ruggle again st tobacco diseases.