An analytical procedure for the simultaneous determination of six selected endocrine disrupter compounds (EDCs: diltiazem, progesterone, benzyl butyl phthalate (BBP), estrone, carbamazepine (Cbz), acetaminophen) was developed by liquid chromatography electrospray ionization tandem mass spectrometry (HPLC-ES-MS/MS). All of the parameters for HPLC and ES-MS/MS systems including mobile phase composition, flow rate, and sample injection volume were optimized to obtain not only the best separation of species interested but also low detection limits. Reverse phase chromatography coupled to ES-MS/MS was used for the separation and detection of EDCs. Formic acid (0.10% ) and 5.0 mM ammonium formate were selected as mobile phase composition in gradient elution. Detection limits for diltiazem, progesterone, BBP, estrone, Cbz, and acetaminophen were found to be 0.13, 0.12, 0.04, 0.13, 0.12, and 0.05 ng/mL, respectively. Influent and effluents from three different wastewater treatment plants located in Ankara, i.e., rotating flat-sheet membrane unit, pilot type flat-sheet membrane unit located at METU Campus and samples from Ankara central wastewater treatment plant were analyzed for their EDCs contents under the optimum conditions.