Abstract: Objective To understand the pathogen characters and change variation trend of viral diarrhea in Guangdong Province and to provide reference for prevention and control of viral diarrhea.Methods Twenty-three sentinel hospitals were collected from 11 cities in Guangdong Province.Every sentinel hospital collected at least 3 stool samples of diarrhea outpatients aged 5 and below and above 5 years, respectively, for rotavirus and norovirus detection.Results A total of 4 644 specimens of diarrhea cases were collected from 23 sentinel hospitals in 2012 in Guangdong Province.Positive rates of rotavirus and norovirus were 13.94% (645/4627) and 22.14% (1028/4644), respectively.The rotavirus-positive rate of cases aged 5 and below (18.60%）was significantly higher than that above 5 years (8.95%) (P<0.01).The norovirus-positive rates had no significant difference between cases aged 5 and below (21.88%) and those above 5 years (22 41%) (P>0.05).The highest rotavirus-positive rate (41 50%, 105/253) presented in January The highest norovirus-positive rate (40.15%, 218/543) was in October.Of 226 specimens randomly selected from 1 028 norovirus-positive ones for gene sequenced, 203 belonged to GII genotype and 23 belong to GI genotype.Among 203 GII genotype strains, 172 were GII-4 genotype (87 as GII.4 Sydney 2012 genotype, 78 as GII.4 2006 b genotype, 4 as GII.4 2010 gonotype, and 3 as unsubtyped).Conclusion The dominant virus of viral diarrhea was norovirus in Guangdong Province in 2012 and relevant to the emergence of GII-4 Sydney 2012 strain.