Phthalates are considered priority pollutants because of their potential adverse effects on ecosystems and human health. The objectives of this study were to determine the occurrence of five phthalates (DMP, DEP, DBP, BBP, and DEHP) in sewage sludge and to determine the seasonal variability of these contaminants at three (Bahceehir, Paakoy, and Tuzla) full-scale municipal and domestic wastewater treatment plants (WWTP) in Istanbul, Turkey. Mass balance was also calculated for DEHP at Tuzla WWTP sludge treatment units. DMP, DEP, DBP, BBP, and DEHP concentrations in sewage sludge ranged from 1.4 to 2.7mg/kg dry weight (dw), 1.1 to 2.8, 0.6 to 4.6, 2.8 to 6.2, 18 to 490mg/kg dw, respectively. Phthalate concentrations from the Bahceehir and Paakoy WWTPs met the limit (100mg/kg dw) of Turkey national sludge regulation and the Europe Union draft of sludge directive for land application, whereas phthalate concentrations from Tuzla WWTP exceeded the maximum permissible concentration. Phthalate concentrations did not show seasonal variations for Bahceehir and Paakoy WWTPs, which receive mainly household wastewater while some fluctuations were observed DEP, DBP, and DEHP at Tuzla WWTP which has a lot of industrial wastewater contribution. The mass balance showed that approximately 17% of DEHP in the primary and secondary sludge was removed by anaerobic digestion, while 43% returned back to the beginning of the WWTP and 40% remained in the dewatered sludge. This study suggests that phthalates in sludge from WWTPs with industrial wastewater contribution may limit the use of sludge for land application.