Twenty-four pigs (Large White × Landrace; 128.2 to 134.1 kg) of similar breeding were utilized in a randomized complete block design to evaluate the effects of dietary supplementation of conjugated linoleic acid on body composition of mature, finished pigs. Pigs were blocked by BW and sex and were randomly assigned and evenly distributed between a treatment (n = 12; TRT) or control group (n = 12; CON) for an 84-d feeding trial. Diets were formulated to be isocaloric and isonitrogenous and consisted of a CON diet of a commercially available concentrate (Producers Cooperative, Bryan, TX) with an additional 2% of the total diet of soybean oil, or the TRT diet that consisted of the same pelleted concentrate with an additional 2% of the total diet of oil containing CLA. The CLA source (BASF Corp., Florham Park, NJ) being utilized contained 55% CLA (mixture of cis-9, trans-11; trans-10, cis-12; and trans-9, trans-11 isomers) yielding a CLA supplementation of 1.1% of the total diet. Oil was top-dressed and mixed into feed immediately before feeding. Pigs were fed at 12-h intervals at 3.5% BW per day in concentrate. Body weight was obtained every 7 d with the intake of concentrate adjusted accordingly. Fat thickness (cm) was measured at 14-d intervals via ultrasonography at the 10th and last ribs. Longissimus muscle area (LMA) was collected via ultrasonography at d 0 and 84. Data were analyzed using the mixed procedure of SAS. Overall effects were analyzed using repeated measures and data from individual days were analyzed using fat thickness from d 0 as a covariate. CLA supplementation had no effect on body composition. Overall, there was no difference between treatments in BW (P = 0.98), 10th rib fat thickness (P = 0.07), last rib fat thickness (P = 0.17), or LMA (P = 0.96). Additionally, there were no treatment × time interactions for the variables measured. These data indicate that CLA supplemented at 1.1% of the diet when mature pigs are fed at 3.5% BW has no effect on body composition or BW. Further studies are needed to fully elucidate dietary CLA supplementation to alter body composition when fed to mature pigs.