A new cobalt complex [Co-3(SIP)(2)(4-PP)(8)(H2O)(6)]center dot 4H(2)O center dot 2(4-PP) (1) with 5-sulfoisophthalic acid sodium (NaH2SIP) and 4-phenyl pyridine (4-PP) as ligands has been synthesized in the mixed solvents of ethanol and water. It crystallized in monoclinic, space group P2(1)/c, with a = 20.9642(9) angstrom, b = 15.6091(5) angstrom, c = 20.0126(8) angstrom, alpha = 90.00 degrees, beta = 115.493(6)degrees, gamma = 90.00 degrees, V = 5911.2(4) angstrom(3), Z = 2, Dc = 1.346 g/cm(-3), F(000) = 2494, the final GOOF = 1.038, R-int = 0.0258 and wR(2) = 0.1793. The complex (1) was characterized by single-crystal X-ray diffraction, magnetic susceptibility and IR spectroscopy analyses. Single-crystal X-ray diffraction shows that complex (1) is trinuclear based on cobalt units. Magnetic susceptibility measurement indicates that complex (1) shows an antiferromagnetic coupling between the Co(II) ions.