A new cobalt(Ⅱ)-radical complex: [Co(im4-py)₂(PNB)₂] (im4-py=2-(4'-pyridyl)-4,4,5,5-tetramethylimidazole-1-oxyl, HPNB=p-nitrobenzoic acid) has been synthesized and characterized by X-ray diffraction analysis, elemental analysis, IR, and magnetic properties. X-ray diffraction analysis shows that the complex exists as mononuclear molecules and Co(Ⅱ)ion is four-coordinated with two radicals and two PNB^- ligands. The magnetic susceptibility study indicates the complex exhibits weak ferromagnetic interactions between cobalt(Ⅱ) and im4-py radical. The magnetic property is explained by the magnetic and structure exchange mechanism.