Enterotoxigenic Escherichia coli is a major cause of diarrhea in neonatal and post-weaning piglets. To determine the most common fimbrial antigens of ETEC in piglets with diarrhea, two investigations were carried out on intensive pig farms in Hubei province, central China. In 2002-2003 fecal samples from neonatal and post-weaning piglets with diarrhea were tested for the presence of the fimbrial antigen K88 and K99 of ETEC by the polymerase chain reaction (PCR). Twenty-three (10.1%) of 227 fecal samples were found to contain fimbrial antigen K88, which was identified as K88ac variant; and 13 (5.7%) samples containing K99. In 2004, another 179 fecal samples from diarrheic piglets, 1 day to 6 weeks of age, were tested for prevalence of fimbrial antigen K88, K99 and 987P. Forty-seven (26.3%) of the 179 samples carried at least one of the ETEC fimbrial antigens. K88 antigen was detected in 20.1%. In the 36 samples known to carry fimbrial antigen K88, 32 (88.9%) contained K88ad; and 4 (11.1%) contained K88ac; none of them carried K88ab. Fimbrial antigens K99 and 987P were detected in 1.1% and 6.1%, respectively. Our data indicate that K88 is the most common fimbrial antigen of ETEC associated with diarrhea in piglets in Central China.