Abstract: In order to study the effect of the addition of tea tree oil in the daily ration on the growth performance and diarrhea of weaned piglets, by setting the basal ration as control (CK group), the feed additive, tea tree oil, of 2, 4 and 8 g·kg^-1 was respectively added to the basal ration (Group A, Group B and Group C) and the weaned piglets were fed for 23 days. Then, the diarrhea and growth performance of the test piglets in the formal experiment period (28 days) were statistically analyzed. The results showed that:adding tea tree oil of 4 and 8 g·kg^-1 to the basal ration could significantly increase the average daily weight gain of piglets (respectively 367.35 and 365.45 g·d^-1) with no significant difference (P>0.05), which was 50.97 and 49.07 g·d^-1 higher than that of CK group with the difference at significant level (P<0.05). Adding tea tree oil of 4 and 8 g·kg^-1 to the basal ration could significantly reduce the diarrhea rate and diarrhea index of piglets with no significant difference (P>0.05). Compared with the CK group, the diarrhea rate decreased by 3.82% and 3.88% respectively, and the diarrhea index decreased by 0.17 and 0.18 respectively with the difference at significant level (P<0.05). It was preliminarily proved that adding tea tree oil, the feed additive, could promote the growth of weaned piglets and reduce the diarrhea of piglets, and 4 g·kg^-1 was the most appropriate addition.