Cobalt doped ZnO nanoparticles were synthesized by microwave irradiation technique for their structural and magnetic properties. Initially the samples were exhibit single phase standard ZnO wurtzite structure (x ≤ 0.1) further Co concentration increase Co3O4 phase was confirmed by X-ray diffraction analysis. The average crystallite sizes of cobalt doped ZnO particles were calculated by Debye-Scherrer formula and are nearly 25 nm. The hexagonal wurtzite structure of ZnO and destroyed cubical Co3O4 were identified in the TEM images. The presence of metal oxide was confirmed by Fourier transform infrared spectral analysis result. The micro-Raman analysis confirmed the existence of Co3O4 phase. Magnetization measurements performed by using vibrating sample magnetometer determine the paramagnetic behavior for the synthesized samples.