In this research, it has been used various nanomaterials and nanostructures for the modification of conventional working electrodes to improve efficiency and sensitivity of the electrochemical sensors. In the first section, the electrochemical behavior and determination of some drugs such as captopril, hydrochlorothiazide, amoxicillin, the alkaloid of thebaine, and RDX high explosive, have been studied on a multi-walled carbon nanotubes (MWCNTs) modified electrode by electrochemical impedance spectroscopy (EIS) and adsorptive stripping voltammetry techniques for the sensitive determination of compounds in the pharmaceutical, human urine or other samples. Here, some sensitive, simple, and time-saving voltammetric procedures were developed for the analysis of mentioned analytes in the real samples. Under optimized conditions, the detection limits of the above compounds are 0.20 mM, 0.77 nM, 0.21, mM, 0.23 mM, and 25.0 nM, respectively. Also a nanocomposite based on the MWCNTs and cobalt hexacyanoferrate nanoparticles has been chemically synthesized and used for the selective determination of diclofenac. In the other section, a new and simple approach based on a continuous pulsed-potential (CPP) method has been employed on then polycrystalline gold electrodes for the preparation of a nanoporous thin film on its surface to enhance electron transfer kinetics and sensitivity of the electrochemical reactions on the conventional gold electrodes, and the resulted pretreated electrode was used for the electrocatalytic determination of metronidazole. In continuing, nanodendrites of silver, as a new electrode material, with interesting electrocatalytic behavior, were synthesized by electrodeposition processes using PEG-400 polymer as a soft template. Then the electrochemical behavior of these products was investigated by voltammetric and EIS methods, and they were compared with usual silver or MWCNTs electrodes. The characterization of all of the prepared nanomaterials, such as Ag nanodendrites, nanoporous gold and others, was investigated by some useful techniques such as X-ray diffraction (XRD), FT-IR, scanning electron microscopy (SEM), atomic force microscopy (AFM), and electrochemical probes.