This study was undertaken to estimate the combining ability in turnip rape through diallel analysis involving five diverse genotypes. A 5 x 5 full diallel crosses study, including the reciprocals, with turnip rape (Brassica rapa L.) was performed to determine both the magnitude of gene action and heterotic performance of the crosses for seed yield and important yield components. Field experiments were conducted at Uludag University, Bursa, Turkey, during the 2008-2009 and 2009-2010 growing seasons. All 20 F1 hybrids and their parents were sown in a randomized complete block design with 3 replicates. During both years, the mean squares of the general combining ability (GCA), specific combining ability (SCA) and reciprocal combining ability (RCA) were statistically significant for all traits evaluated. The parent Malvira was a good general combiner because this parent had the highest significant positive GCA effects for all the characteristics evaluated. In addition, Lenox proved to be a good general combiner for plant height. The significant positive mid-parent and high-parent heterosis values were obtained with several crosses in important yield components. In conclusion, the parents used in this study exhibited positive GCA effects for seed yield. Therefore they could be considered as promising parents in the production of F1 hybrids and in further breeding studies.