Our study examined if dietary long-chain polyunsaturated fatty acids (LCPUFA) have an impact on oxidative stress in preterm infants. Serum malonyldialdehyde (MDA), total peroxide concentrations, and total antioxidant capacity were determined at mean (standard deviation [SD]) 34.7 (10.9) days of life in 104 healthy preterm infants (gestational age, 32.6 [2.9] weeks; birthweight; 1605 [285] g) who were randomly assigned to be fed since birth either a formula containing LCPUFA (arachidonic and docosahexaenoic) (group A, n = 50) or a LCPUFA-free formula with identical compositions for other nutrients (group B, n = 54). Clinical and anthropometric characteristics did not differ significantly between the two groups. Mean (SD) serum MDA levels did not differ significantly between groups A (0.23 [0.04] micromol/L) and B (0.22 [0.05] micromol/L). The concentrations of total peroxides were below the detection limits of the assay in 41 of 50 (82%) infants of group A and 43 of 54 (79%) infants of group B and not significantly different between the two infant groups. No difference was observed in serum total antioxidant capacity between groups A (340.0 [46.2] micromol/L) and B (354.7 [46.5] micromol/L). We concluded that supplementation of infant formulas with LCPUFA does not affect lipid peroxidation in healthy preterm infants.