Abstarct: In this thesis, the structural, magnetic and electrical properties of La0.8Sr0.2MnO3 nanomanganites have been studied. Nanoparticle were synthesized using cost and simple effective microwave radiation processes. In order to form the pure crystalline phase and to study the sintering temperature effect on physical properties , the obtained powder were calcined at different temperatures. The structural investigation showed that all samples have a rhombohedral structure with R-3C space group. The magnetic study of the samples using DC magnetization and AC susceptibility measurements, indicated that the magnetic phase transition becomes broad with decreasing of the particle size and the Curie temperature has been considerable shifted to the lower temperatures. Also reduction of magnetization was observed with decrease of the particle sizes. This behavior can be described by core-shell model and magnetic dead laxyer thickness estimated to be about 2.84nm for 30nm grain size sample. Fitting the experimental data with Neel-Brown and Vogel-Fulcher models confirmed the existence of medium to strong interaction between the nanoparticels. Also, the obtained results show that the superparamagnetic interaction behavior is predictable at above the blocking temperature. The experimental data was fitted by critical slowing down model and the results suggested the existence of super-spin-glass behavior in our samples. The electrical properties of the samples were studied by resistance measurements versus temperature and the effect of particle size on resistivity and mextal-insulator transition were investigated. Also, the resistivity data in mextalic region were fitted with exist theoretical models.