This article evaluated the effects of supplemental probiotic Bacillus subtilis (Bs) ATCC 6051a (1.6×109 cfu/mL) in diets for weaned piglets on their performance and on the occurrence of diarrhoea. Sixty piglets, 30 ±3 days old with initial bodyweight of 8.41±0.92 kg, were allotted randomly to six pens of ten piglets. There were two replicates of each treatment, namely a control diet (C), a diet supplemented with 1% Bs (E1), and a diet supplemented with 3% Bs (E2). Feed was provided ad libitum as flour in two meals per day. Feed materials were examined for total numbers of fungi, aerobic mesophilic bacteria (TNG), Coliforms, Escherichia coli and Salmonella spp. The addition of Bs did not influence (P >0.05) bodyweight (BW) or average daily weight gain (ADWG). However, across the experimental period ADWG was greater in E2 and E1 than in C (>1.12 and 1.08 times compared with C). Feed intake (ADFI) by pigs fed C was greater than pigs fed E1 and E2. Feed efficiency was higher in E1 and E2 than the C diet. Addition of 1% Bs decreased (P<0.05) diarrhoea occurrence around 8% compared with C, and 4% compared with 3% Bs. A total of 23.4% of the piglets produced soft faeces. Diarrhoea scores of 2 (mild diarrhoea) and 3 (severe diarrhoea) were observed in 43.75% and 32.81% of the pigs. No differences (P >0.05) were detected between the treatments. The results suggested that E1 could positively affect growth performance and mitigate the occurrence of diarrhoea.