This study aimed to investigate the effects of dietary spray-dried plasma (SDP) on the gut microbiota of lactating sows and their piglets. A total of 12 sows were randomly assigned to one of two dietary treatment groups in a completely randomized design. The treatments were a sow diet based on corn and soybean meal (CON), and a CON diet with an added 1% SDP. The sows were fed the dietary treatments from d 30 before farrowing to weaning (d 28). The fecal samples of three sows from each treatment and two of their randomly selected piglets were collected to verify their fecal microbiota. There were no differences in the alpha diversity and distinct clustering of the microbial communities in the sows and their piglets when SDP was added to the sow diets from late gestation to weaning. The fecal microbiota of the lactating sows and their piglets showed a higher relative abundance of the phylum Bacteroidota and genus and and showed a lower relative abundance of the phylum Bacillota and genus , , and in the sows fed the SDP diet than those fed the CON diet. Overall, these results show that the addition of SDP to the sow diet during lactation altered the gut environment with positive microbial composition changes. These results were similar in the nursing piglets, suggesting that the control of the sow diets during lactation may contribute to the intestinal health and growth in piglets after weaning.