Pure ZnO and cobalt doped ZnO nanocrystals were synthesized using the polymer-pyrolysis route. Samples with a molar ratio of Co(NO3)(2):Zn(CH3COO)(2) in the range 0, 1, 3, 5, and 7 % were synthesized. The structural, compositional, optical, surface, and magnetic properties of these nanocrystals have been determined. For this purpose characterization techniques including X-ray diffraction (XRD), Energy dispersive X-ray analysis, Fourier transform infrared (FTIR), UV-Vis absorption, field-emission scanning electron microscopy, and vibrating sample magnetometer system were used. XRD and FTIR results showed that both Co-doped and undoped ZnO nanocrystals crystallized in a ZnO wurtzite structure. The lattice constants for the Co-doped ZnO samples are very close to that of the pristine ZnO. Also, Co ions are replacing the Zn position in ZnO lattice without much change in the volume of the unit cell. High-quality crystalline sample was confirmed for the Co-doped samples with molar ratio 1 %. The incorporation of Co ions into the Co-doped ZnO lattice in Zn sites was confirmed from UV-Vis results. Optical peaks around 574, 612, and 666 nm were detected, which interpreted to the d-d electronic transitions of the tetrahedrally coordinate of Co2+ ion. Undoped and Co-doped samples show room temperature ferromagnetic (RTFM) behaviors and their magnetic parameters showed Co concentration dependency and thus these results fit the requirements of magnetic applications.