Abstract: The aim of the study was to investigate the effects of ultra-fine herbal feed additive at a proportion of 0.5% on growth performance and diarrhea rate in weaned piglets.Single factor completely randomized design was used for the experiment.A total of 54 healthy weaned piglets [（9.50 ± 0.63） kg,28 days old] were selected and randomly divided into three treatment groups including two experimental groups and one control group,18 in each group（half male and half female） and three replicates in each group.Statistical analysis showed no significant difference in body weight between the groups（P0.05）.The piglets in the control group were fed basic diet not containing any drug like antibiotic.Those in the group Ⅰ were fed with the basic diet supplemented colistin at a dosage of 0.02%.Those in the group Ⅱ were fed with the basic diet supplemented ultra-fine herbal feed additive at a proportion of 0.5%.The feeding period was 30 d.The results showed that the average daily feed intake and daily gain of the group Ⅱ were significantly higher than that of the control group（P0.05）.The feed conversion rate and diarrhea rate of the group Ⅱ were significantly lower than that of the control group（P0.05）.And the feeding effects were better in the group Ⅱ than in the group Ⅰ.Therefore,in the experimental conditions,the ultra-fine herbal feed additive,an alternative of antibiotic feed additive,can ensure the healthy growth of weaned piglets.