The purpose of this study was to determine the effects of inbreeding on seed set in forage watermelon genotypes obtained from different sources. The study, conducted in 2017, used watermelon genotypes from different sources under Konya ecological conditions. The planting of seeds in pots in the greenhouse produced seedlings, further planted in the trial area with a 200 cm × 100 cm spacing in May 2017. From 66 forage watermelon genotypes used in the study came fruits from both inbred and open pollinated genotypes flowers on the same plant. In 40 of these genotypes, the seed yields obtained in inbreeding appeared higher than the seed yields obtained in the open pollination. In the study, the seed yield (127.6 g fruit–1) acquired from inbreeding was 16.3% higher than the average seed yield (109.7 g fruit–1) from open pollination. This rate showed the success rate in inbreeding was high, with no self-incompatible in the forage watermelon genotypes used in the study, and inbreeding had no negative impacts on pollination, fertilization, fruit set, and seed yield.