The effect of fruit thinning time and thinning rate on flowering, fruit yield and fruit quality of clementine trees (Citrus clementine Hort. ex Tanaka) was investigated during three successive seasons 2017/2018, 2018/2019 and 2019/2020. Data recorded only during 2018/2019 and 2019/2020 seasons. Thinning applied at three different times on 1^st June, 15^th June and 30^th June. Fruit thinning rate were performed when the fruit diameter reached about 25-30 mm, as hand thinning by removing 0, 25 or 50% of fruit number/shoot per tree. Clementine trees grafted on sour orange were studied in an 8-years-old orchard in Al-Sheikh Zuwaid destrict, North Sinai, Egypt. The experimental treatments were arranged in a complete randomized block design. The results obtained showed that thinning clementine trees on 1^st June exhibited the greatest value for each of No. inflorescences/ one year shoot, flowers number/ one year shoot, fruit set (%), No. remaining fruits, fruit yield (kg/tree) and fruit weight (g), fruit volume (cm³), fruit length (cm), fruit width(cm) in both seasons while 15^th June time thinning gave the highest T.S.S.(%) and segments number, on the contrary 15^th June time thinning gave the highest juice acidity(%). Hand thinning at 50% increased all fruit yield and quality parameters except the juice acidity (%) that induced with non- thinning tree (control). Finally, on 1^st June, removing 50% of fruit number/shoot per tree caused a significantly increase in flower number, fruit set (%), fruit number, fruit weight, yield/tree and improved the commercial classification of mandarin fruits compared to unthinned ones.