NiO nanoparticles were in situ formed in a new metalorganic framework (MOF), [Ni-3(pyip)(2)(HCOO)(2)(H2O)(2)](n) [1; H(2)pyip = 5-(pyridine-4-yl)isophthalic acid], which was characterized by Fourier transform infrared spectroscopy, elemental analysis, thermogravimetric analysis, transmission electron microscopy, and powder and single-crystal X-ray diffraction. The MOF 1 shows a 3,6-connected three-dimensional rtl topology network with a topological symbol of (4.6(2))(2)(4(2).6(10).8(3)). Magnetic property studies showed that the combination of NiO nanoparticles within the magnetic MOF leads to the occurrence of long-range magnetic ordering below a critical temperature of 18 K.