In lactating sows, a great proportion of the energy consumed is prioritized to milk production and synthesis of its components, resulting in an intense catabolism of body stores. As shown in dairy cows, ewes and goats, C18:2 trans-10,cis-12 conjugated linoleic acid (CLA) decreases milk fat synthesis and it may be an option to minimize the energy costs of lactation without compromising the piglet performance. This study evaluated the effect of CLA on sow milk yield and composition, and on piglet performance. Twenty multiparous sows from a commercial lineage, with a mean body weight (BW) of 200 ± 10 kg were randomly assigned to one of the 2 treatments (n = 10/treatment) for 18 d: (1) Control (no fat) and; (2) 1% of CLA (29,9% of trans-10,cis-12 and 29,8% of cis-9,trans-11) mixed in the ration. The diet was formulated to meet the nutritional requirements for the breed. Sows were kept in a controlled environment (temperature, humidity, and ventilation) and the CLA treatment was administered from d 7 through d 25 of lactation. Milk samples were collected from all sows from d 0 to d 25 to evaluate milk concentrations of fat, protein, lactose, and total solids. Data were analyzed as a complete randomized design using the Mixed Procedure of SAS. The model included the random effect of sow, and the fixed effects of treatment and d 0 measurements, the latter used as a covariate and removed if not significant. Compared with Control, CLA treatment decreased milk fat content by 20% (Control = 6.2 vs. CLA = 4.9%, P = 0.004). In addition, CLA reduced milk protein content by 13.7% (Control = 5.04 vs. CLA = 4.35%, P = 0.001). However, milk lactose content tended to be higher in the CLA group (Control = 5.6 vs. CLA = 5.8%, P = 0.08). Despite the reduction in fat content, the weight of piglets at weaning was not different between treatments (Control = 7.8 vs. CLA = 7.9 kg, P = 0.60). These results indicate that CLA reduces the milk fat content without negatively affecting litter performance.