A prospective study was done by the examination of nasopharyngoscope, reaction of EB virus's antigens and antibodies, nasopharyngofibroscope, pathological and EB virus's DNA, EBERs, etc. of about 100000 persons in high risk area of NPC in Guangdong Province, China from 1986 to 1995. If any one of the following four conditions is present in some persons, i.e., (1) EBV VCA/IgA titer>l:80, (2) EBV EDAb>60%, (3) Dual or triple positiveness in VCA/IgA, EA/IgA and EDAb, (4) Any one of VCA/IgA, EA/IgA and EDAb keeps high titer or going up, they should be regarded as in precancerosis of NPC. The moderate or severe heteroplasia and heterometaplasia of nasopharyngeal mucosa are the precancerous lesions of NPC. Some individual who is in precancerosis or with precancerous lesion should be regarded as the high risk population of NPC. The results are of important scientific basis for screening and second degree prevention of NPC.