Preceding monitoring reports indicated that di (2-ethylhexyl) phthalate (DEHP), a commonplasticizer, was found in the samples of suspended sediment and water collected from the lowerpart of Chao Phraya River. In this continuing study, the suspended sediment and water samplesfrom the Chao Phraya Delta were collected twice a year in January and July during January 201 1 -July 2013. The analyses were performed for both DEHP and Diethyl Phthalate (DEP). Overallresults showed that concentrations of both DEHP and DEP in the water samples were relativelyhigher than those in the suspended sediment samples. The concentrations of DEHP and DEP fromall sampling periods in the water samples ranged from 1.58 - 27.55 pg/L and from 0.64 - 2.59ug/L, respectively, whereas the concentrations of DEHP and DEP from all sampling periods in thesuspended sediment samples ranged from 0.01 - 26.82 mg/g and from 0.01 - 1.93 mg/g,respectively. The concentrations of both DEHP and DEP in both suspended sediment and watersamples were relatively higher in the samples collected during lower discharge period of the ChaoPhraya River in July. The results indicated that sediment transport system could play an importantrole in the dispersion of both DEHP and DEP. The ecological risk assessment indicated that for thecurrent level of contaminations the risk did not exceed the acceptable level.