The Valencia orange is a high quality fruit grown in Turkey; however, small fruit size resulting in poor packouts is common in Valencia oranges. Small fruit size is the main factor limiting the marketing of Valencia oranges; thus, synthetic auxins are commonly used to enhance the size of citrus fruit. The objective of the present study was to observe the effects of 3,5,6-trichloro-2-pyridyloxyacetic acid (3,5,6-TPA) on fruit size, yield and quality of Valencia oranges from 29-year-old trees budded on sour orange rootstock in Adana, Turkey in 2006. The application of 3,5,6-TPA to the entire tree was from 8(th) to 11(th) week after anthesis during June drop (JD). Following 3,5,6-TPA treatments, different combinations were used in the experiment: T-1 2 tablets per 100 litres applied just after the end of June drop (JD), T-2 2 tablets per 100 litres applied 5-7 days after the end of JD, T-3 3 tablets per 100 litres applied 5-7 clays after the end of JD, T-4 4 tablets per 100 litres applied 5-7 days after the end of JD, T-5 3 tablets per 100 litres applied 10-14 days after the end of JD and control trees receiving no 3,5,6-TPA (T-0). As a result, all treatments with 3,5,6-TPA reduced fruit yield, except for trees treated at the highest rate (T5). Compared to control trees, all applications of 3,5,6-TPA increased the number of large, commercially valuable Valencia oranges (>70.00 mm and 65.01-70.00 mm). Except for the titratable acid content (TA) and total soluble solid/TA ratio (TSS/TA), the internal characteristics of the fruit were not affected by treatment with 3,5,6-TPA. Generally, total acidity was decreased by treatment with 3,5,6-TPA. The results of the present study revealed that 3,5,6-TPA can be used to improve the size of Valencia fruitlets during the June drop.