Increasing the high-quality yield of a cultivated fruit species is an important method for improving its ability to compete in world markets. A high fruit yield and an increase in the proportion of marketable fruit will aid in obtaining the market objectives for the species. To this end, pruning is a very important horticultural practice. Mechanical pruning has numerous advantages over classical pruning, such as enabling control over the tree size and providing mechanization in large and dense orchards that make hand pruning applications difficult and expensive. Mechanical pruning is used widely in developed countries for many horticultural crops including citrus. In Turkey, established citrus orchards generally have dense foliage and planting, making pest and disease management very difficult. It is necessary to improve orchard management and to introduce new technologies to production areas. Thus, the introduction of mechanical pruning into Turkish citrus orchards may have the potential to improve production. In this study, our aim was to determine the effects of mechanical pruning applications on the 'Star Ruby' grapefruit, the most commonly grown grapefruit variety in Turkey. Our pruning treatments included the following: 1) hedging, 2) topping and 3) hedging and topping. The study was carried out with thirteen-year-old Star Ruby grapefruit trees that were budded onto local sour orange (Citrus aurantium L.) rootstock. The trees were planted using semi-dense spacing (8 m x 4 m) in orchards established in Adana between 2004 and 2006. The orchard was then mechanically pruned each year. Our results indicate that the highest yield was obtained from the topping-hedging treatment, while the lowest yield was obtained from the topping treatment. Mechanical pruning, especially the topping treatment, increased the fruit size as compared to the control. Taken together, our results demonstrate that mechanical pruning is a potential option for grapefruit planted in semi-dense orchards. The small decrease in yield due to the mechanical pruning may have been caused by the repeated application over three years.