In order to elucidate the effect of fermentation bed on bacterial growth in gastrointestinal tracts of weaned piglets,the changes of Escherichia coli and lactic acid bacteria in weaned piglets raised in pens with fermentation bed and cement floors were analyzed kinetically.Three piglets in each treatment were slaughtered at 0 d,21 d and 42 d respectively.The mucous layer and the content of the stomach,ileum,cecum,and colon as well as the cushion of fermentation bed,were sampled at each time point for bacterial detection.As a result,the number of E.coli decreased gradually with time,for example,the number of E.coli collected from the colon of the piglets raised on the fermentation bed decreased from 107 at the beginning to 105.However,the amount of lactic acid bacteria in gastrointestinal tracts decreased at the early stage but increased at the later stage,such as,the number of lactic acid bacteria collected from the ileum of piglets raised on the fermentation bed was 109 at the beginning,then decreased to 108  and increased 1010  at last.The fermentation bed did not alter the tendency of bacterial fluctuation.Meanwhile,the high number of lactic acid bacteria in the fermentation bed cushion did not contribute to the growth of these bacteria in gastrointestinal tracts of weaned piglets.In addition,the species and number of potential pathogens in fermentation bed would increase with the lengthening of utilization time with no E.coli in the bottom of fermentation mattress material and 107 on day 42.