This study investigated the effects of dietary supplementation with different levels of grape seed oil (GSO) on growth performance, feed conversion ratio (FCR), carcass characteristics, and internal organ weights in quails. A total of 400 mixed-sex Japanese quail chicks (Coturnix coturnix japonica) at three days of age were randomly assigned to four main groups (100 birds each), with each leading group further divided into five subgroups of 20 chicks. During the experimental period, GSO supplementation did not have a statistically significant effect on feed intake (FI) (p>0.05). However, in specific periods (particularly at 0.1% and 0.2% supplementation levels), significant improvements in FCR and average daily gain (ADG) were observed (p<0.05). Notably, during the early growth phase (days 1–21), GSO supplementation led to a significant increase in ADG. Regarding carcass characteristics, only the dorsal region weight showed a significant increase at the 0.1% GSO level (p<0.05). In terms of internal organ weights, significant differences were detected only in heart and proventriculus weights, while no statistically significant differences were found in other organs or abdominal fat percentage. The improvements in growth performance, digestive efficiency, and oxidative balance are believed to be linked to the linoleic acid and phenolic compounds present in GSO. In conclusion, low levels of GSO supplementation may enhance early growth performance and feed efficiency in quails, while its long-term effects are limited.