This experiment aimed to evaluate the effects of using sugarcane bagasse (SB) as a substitute for soybean hulls and wheat bran in the diet of pregnant sows on their reproductive performance and gut microbiota. A total of seventy-two primiparous sows were randomly divided into four treatment groups, with eighteen replicates of one sow each. The sows were fed a basal diet supplemented with 0% (CON), 5%, 10%, and 15% SB to replace soybean hulls from day 57 of gestation until the day of the end of the gestation period. The results showed that SB contains higher levels of crude fiber (42.1%) and neutral detergent fiber (81.3%) than soybean hulls, and it also exhibited the highest volumetric expansion when soaked in water (50 g expanding to 389.8 mL) compared to the other six materials we tested (vegetable scraps, soybean hulls, wheat bran, rice bran meal, rice bran, and corn DDGS). Compared with the CON, 5% SB significantly increased the litter birth weight of piglets. Meanwhile, 10% and 15% SB significantly increased the rates of constipation and reduced the contents of isobutyric acid and isovaleric acid in feces. Furthermore, 10% and 15% SB significantly disturbed gut microbial diversity with increasing and decreasing and genera in feces. Interestingly, had a significant negative correlation with isobutyric acid, isovaleric acid, and fecal score, while and had a positive correlation with them. In conclusion, our study indicates that 5% SB can be used as an equivalent substitute for soybean hulls to improve the reproductive performance of sows without affecting their gut microbiota.