The objective of this study was to investigate the effects of dietary supplementation with a Bacillus-based probiotic complex on growth performance, nutrient digestibility, blood metabolites and faecal microbial communities in weaned piglets. A total of 144 crossbred weaned pigs (Yorkshire × Landrace) × Duroc, 28 days old, were randomly allocated to one of four dietary treatments. Each treatment was replicated in six pens, with six pigs per pen (three barrows and three gilts). The treatments included a basal diet (CON), and a basal diet supplemented with graded levels (0.1%, 0.2% and 0.3%) of a probiotic complex consisting of Bacillus subtilis (1.0 × 10⁹ CFU/g) and B. licheniformis (1.0 × 109 CFU/g). The experimental diets were administered in a mash form for six weeks. The results showed that the gain-to-feed ratio (G:F) on days 0–7, and G:F and average daily weight gain (ADG) during days 22–42 and 0–42 increased linearly with higher proportions of added probiotics (P < 0.05). Furthermore, the 0.3% probiotic group exhibited significantly higher ADG and G:F ratio on days 0–42 compared to the CON group (P < 0.05). The concentrations of NH₃ and H₂S in faeces were also significantly lower in the 0.3% probiotic group compared to the CON group (P < 0.05). In conclusion, the addition of the 0.3% Bacillus probiotic complex to the diet resulted in an increase in average daily weight gain and the feed-to-gain ratio of weaned piglets, as well as a reduction in faecal noxious gas emissions.