A study was conducted to determine effects of mannan oligosaccharide (MOS) supplementation of the diets of sows and their offspring on maternal and offspring performance and immune status. Sixty multiparous sows were fed either a control diet (sCON, n = 30) or a diet containing 400 mg/kg MOS (sMOS, n = 30) from d 86 of gestation until the end of lactation. On d 7 of age, offspring were assigned within sow treatments to the piglet basal diet (pCON) or the piglet basal diet + 800 mg/kg MOS (pMOS) for 28 d. Thus, the offspring treatments were sCON-pCON, sCON-pMOS, sMOS-pCON, and sMOS-pMOS, 15 litters per treatment. No dietary effect was observed on the number of total piglets born and born alive and the piglet weight at birth. Serum-specific antibody concentrations of porcine reproductive and respiratory syndrome, classical swine fever, and porcine pseudorabies of sows and immunoglobulins concentrations in colostrum and milk were not affected by sow dietary MOS (P > 0.05). However, the weaning to estrus interval of sows was shortened significantly in the sMOS treatment compared with the sCON treatment (P = 0.05). The weaning weight (P = 0.03) and pre-weaning weight gains (P = 0.01) of piglets from the sMOS were greater than those from the sCON. Piglets from sMOS had higher serum concentrations of IgA (P < 0.01), IgG (P < 0.01), complement 3 (C3) (P < 0.01), lysozyme (LYZ) (P < 0.01) and complement 4 (C4) (P = 0.05) at weaning, as well as C3 (P < 0.01) and LYZ (P < 0.01) on d 35 of age. MOS supplementation of piglet diet improved both pre- and post-weaning weight gain (P < 0.01) and increased serum concentrations of IgA (P = 0.01) and IgG (P = 0.01) at weaning, as well as C3 (P < 0.01), LYZ (P < 0.01) and C4 (P = 0.01) on d 35 of age. Piglets of the sMOS-pMOS group had higher body weight and better immune statue at weaning and on d 35 of age compared with other groups. These results indicate that supplementing sow diets with MOS during late gestation and lactation improved the growth potential and immune responses of nursing piglets. Furthermore, dietary addition of MOS to pre- and post- weaning piglets also has potential growth and immune-promoting effects.