In this work we report synthesis and magnetic characterization of cobalt doped ZnO nanoparticles (with different percent of doped cobalt oxide). Synthesis of the materials was carried out at room temperature by polyacrylamide-gel method, using zink sulfate and cobalt nitrate as source materials, acrylamide as monomer and N,N-methylene bisacrylamide as a lattice reagent. Characterization of the samples were performed using XRD, SEM, TEM, UV and photoluminescence (PL) studies. The X-ray diffraction patterns obtained showed formation of wurtzite ZnO structure with no secondary Co phases. The EDS measurements were employed to investigate the composition of the samples and showed the presence of Zn and cobalt elements detected. The optical absorption spectra showed internal d-d transitions related to Co2+ incorporated on the Zn lattice site of ZnO structure. The red-shift of the band-gap edge has been attributed to a merging of donor and conduction bands due to the Co doping. The magnetic behavior of prepared cobalt doped samples was finally investigated at room temperature using vibrating sample magnetometer (VSM). The results show that, the Co doped ZnO. Nanoparticles with 2at% CoO is ferromacnetic at RT. This magnetic property is greatly suppressed and replaced by a paramagnetism behavior at higher doping levels.