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 8th to 11th week after anthesis during June drop (JD). Following 3,5,6-TPA treatments, different combinations were used in the experiment: T1 2 tablets per 100 litres applied just after the end of June drop (JD), T2 2 tablets per 100 litres applied 5-7 days after the end of JD, T3 3 tablets per 100 litres applied 5-7 days after the end of JD, T4 4 tablets per 100 litres applied 5-7 days after the end of JD, T5 3 tablets per 100 litres applied 10-14 days after the end of JD and control trees receiving no 3,5,6-TPA (T0).