This work describes the development of a voltammetric sensor for diazinon pesticide determination based on diazinon reduction on glassy carbon electrode (GCE) surface modified with multi walled carbon nanotubes covered by TiO2 nanoparticles (MWCNTs/TiO(2)NPs). Voltammetric investigations were carried out by cyclic voltammetry (CV), linear sweep voltammetry (LSV), differential pulse voltammetry (DPV) and square wave voltammetry (SWV). Prepared nano-composite of MWCNTs/TiO(2)NPs was characterized with scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDX) techniques. Nanocomposite of MWCNTs and TiO(2)NPs showed suitable synergic electrocatalytical properties in diazinon reduction which resulted the completely sensitive determination of diazinon in laboratory samples and real samples including city piped water and agricultural well water. Linear range, limit of detection (LoD) and limit of quantitation (LoQ) obtained by developed sensor were 11-8360 nM, 3 nM and 10 nM successively which were quite satisfying in compared to other works reported about diazinon determination. Response time, Repeatability and stability of sensor were examined and found completely suitable. Moreover electrode modification method was very fast, inexpensive and easy to follow.