A new one-dimensional (1D) chain antiferromagnet Co(ox)(bib)·H₂O 1 (ox = oxalate; bib = 1,4-bis(imidazole-1-yl)benzene) has been successfully synthesized under hydrothermal condition and characterized by single crystal X-ray crystallography, powder X-ray diffraction, thermogravimetric analysis, Fourier transform infrared (FTIR) spectroscopy, magnetic susceptibility, and heat capacity measurements. The Co^II ion is connected by oxalate ions in trans-configuration to form 1D Co^II–ox–Co^II spin chains, which are further separated by the long organic molecule bib. The magnetic susceptibility curve shows that 1 exhibits a feature of broad maximum around 29 K, indicating strong antiferromagnetic interactions with short spin–spin correlations along the spin chains. However, no long-range order is observed due to the negligible interchain interactions through bib ligand and weak hydrogen bonds, which is further confirmed by the heat capacity data. The intrachain interaction J of −8.4 K is estimated. Both magnetic susceptibility and heat capacity results indicate that 1 exhibits a good 1D magnetism.