Date palm is an important tree species in arid and semi-arid regions of the world due to its edible fruits. However, date palm seeds are considered as by-products and are not used. The present study investigated seed morphology, oil content and composition and antioxidant activity of six Iraqi date palm cultivars (Barhi, Zahdi, Hellaoui, Maktoum, Khestawi and Usta Umran). Significant differences were detected for seed length (1.67–2.37 cm), seed width (0.52–0.66 cm) and seed weight (0.57–0.85 g) and seed oil (7.77–9.25%) content between the cultivars. After extraction of seed oils, fatty acids composition, phenolics, tocopherols and antioxidant capacity of seed oils were determined. A total of 24 fatty acids were detected and oleic acid (40.5–46.3%) was the predominant fatty acid, but lauric (17.6–23.5%), myristic (10.2–13.4%), palmitic (9.3–10.6%) and linoleic (7.1–8.8%) acids were also present. The total phenolics content of seed oils were between 42.95 to 206.89 μg gallic acid g−1. The antioxidant capacity of seed oils showed significant differences as assessed by CUPRAC and DPPH methods. The total tocopherol content of date palm seed oils ranged from 178.1 to 424.3 mg L−1 and showed cultivar dependent variation for tocopherol types. The main tocopherol types were β- and γ-tocopherols, α-tocopherol was present in small amounts in all seed oils, but δ-tocopherol was only detected in two oil samples. Principal components analysis was used to investigate the correlations between seed morphology, oil composition and antioxidant activities, and the results showed that seed oil composition largely depended on cultivars. The research indicates that date palm seeds, a by-product, have different oil compositions with high nutritional value among the cultivars.