To evaluate the effects of glutamine (Gln) supplementation on sow performance during late gestation and lactation and their offspring, eighty pregnant, multiparous sows of a commercial hybrid line were used in a completely randomized, 2 × 2 experimental design at the end of gestation and lactation, respectively. Females were subjected to a control diet or a Gln-supplemented diet (1% of L-glutamine) from 85 d of gestation until farrowing. During lactation, the dietary treatment groups were CON_C: without Gln supplementation; CON_G: Gln only during lactation; GLN_C: Gln only during gestation; GLN_ GLN: Gln during gestation and lactation. At 105 d of gestation, there was no statistical difference regarding the body weight of the sows, however, sows fed the Gln-supplemented diet had greater backfat thickness at P1 and loin depth at P2 than control sows. Placental weight and efficiency showed no effect between treatments. Litters born from Gln-supplemented sows tended to be heavier at birth compared to control litters, reducing the probability of piglets weighing less than 1.5 kg. In addition, litters from supplemented sows had a lower standard deviation of BW at birth. There were no effects of dietary treatments on the performance of sows and offspring during the lactation period. Maternal Gln supplementation during late gestation improved piglet weight and litter uniformity at birth without affecting sow body composition after farrowing.