The objective of this work to evaluate the synergetic influence of UV and UV/H2O2 in the decomposition of carbaryl in the aqueous medium, various UV irradiation time in a range from (15-240 min) were investigated in the presence and absence of H2O2, for the removal of carbaryl (CBL) from an aqueous medium. The Gas-Chromatography coupled with mass spectrometry (GC-MS) and ion chromatography (IC) were applied to define the by-products and ionic species. The chemical properties such as total acidity, dissolved oxygen, and pH values were evaluated before and after irradiation in the presence and absence of H2O2. It was found that UV/H2O2 method has higher efficiency on the removal of carbaryl than UV irradiation alone. The complete mineralisation of CBL takes place at irradiation time 75 min using UV/H2O2. Decomposition pathway modelling for carbaryl was suggested based on the results obtained.