The objective of this study was to evaluate the effect of dietary plant oils rich in 18:2n-6 (POLA; including safflower, sunflower, corn, soybean and cottonseed oils) on milk fatty acid (FA) profile in lactating dairy cows, using meta-analysis and meta-regression methods. A total of 20 studies were identified with 27 comparisons between treatment and control groups, which met the selection criteria and included in the analysis. Two levels of POLA supplement (less and more than 30 g/kg diet DM) were evaluated in this meta-analysis. Supplementation of cows with 20 g POLA/kg diet DM reduced milk fat 6:0–16:0, enhanced 18:0, cis (Δ9–12, and 15) and trans 18:1 (Δ6−14), 18:2n-6, cis-9,trans-11 CLA and trans-10,cis-12 CLA concentrations. The weighted mean differences for milk fat content of 16:0, cis-9 18:1, 18:2n-6 and cis-9,trans-11 CLA were –5.687 (95% confidence interval (CI) = –7.558 to –3.816), 3.194 (95% CI = 1.139 to 5.249), 0.810 (95% CI = 0.384 to 1.236) and 0.467 g/100 g total FA (95% CI = 0.281 to 0.653), respectively. Inclusion of 20 g/kg DM POLA had no effect on milk 4:0 and 18:3n-3 concentrations. Results of meta-regression showed that dietary 18:2n-6 content explained more than 55% of the variation in 8:0–15:0 results. Dietary FA content, amount of grain in the basal diets and parity were the sources of heterogeneity for milk cis-9 18:1. Milk trans-11 18:1 increased with increased dietary 18:2n-6 content and forage level of basal diets. Estimated effect size of milk 18:2n-6, trans-10,cis-12 CLA and 18:0 were greater in safflower > sunflower > corn > soybean and > cottonseed oils. In conclusion, feeding 20 g POLA/kg diet DM lowered milk fat 16:0, increased cis-9 18:1, 18:2n-6, cis-9,trans-18 CLA, without any changes on 4:0 and 18:3n-3.