The presence of 11 virulence-associated genes in Campylobacter jejuni isolated from chickens at different stages of their development was examined by PCR. Multiple groups of C. jejuni were colonized in one chicken at the same time. Two hundred thirty one C. jejuni in total were isolated from the same group at four different ages and 12 groups of C. jejuni possessing of 11 virilence-associated genes were observed. Eleven, eight, five and three groups of C. jejuni were detected at 21, 28, 42 and 56 days after hatching, respectively. The variation of Campylobacter groups was reduced as the chicken developed and one group of C. jejuni became predominant.