This study was conducted to evaluate the effects of dietary conjugated linoleic acid (CLA) on the performance of lactating sows and piglets as well as the immunity of piglets suckling from sows fed CLA. Eighteen multiparous Duroc sows with an average body weight (BW) of $232.0{pm}6.38kg$ were randomly selected and assigned to two dietary treatments (n = 9 for each treatment), control (no CLA addition) and 1% CLA supplementation. For the control diet, CLA was replaced with soybean oil. Experimental diets were fed to sows during a 28-day lactation period. Litter size for each sow was standardized to nine piglets by cross-fostering within 24 hours after birth. Sow milk and blood samples were taken from sows and piglets after 21 and 27 days of lactation, respectively. Loss of BW was significantly (p < 0.05) higher in sows fed control diet compared to sows fed CLA diet. Piglet weights at weaning and weight gain during suckling were significantly (p < 0.05) higher in sows fed CLA compared to sows fed control diet. Serum non-esterified fatty acid (NEFA) and urea nitrogen concentrations were significantly (p < 0.05) lower in sows fed CLA than in sows fed soybean oil. IgG concentrations of the groups supplemented with CLA increased by 49% in sow serum (p < 0.0001), 23% in milk (p < 0.05), and 35% in piglet serum (p < 0.05) compared with the control group. Sows fed CLA showed an increase of 10% in milk yield compared with sows fed soybean oil (p < 0.05), even though there was no difference in daily feed intake between the treatments. Milk fat content was significantly (p < 0.05) lower in sows fed CLA than in sows fed soybean oil. Solid-not-fat yield was significantly (p < 0.05) higher in sows supplemented with CLA than in sows fed control diet and also protein-to-fat ratio in milk was significantly (p < 0.05) higher in sows fed CLA compared with the control group. The results show that CLA supplementation to sows increased milk yield without losing BW during lactation, whereas soybean oil supplementation resulted in severe BW loss.