The magnetic properties of Co(N 3) 2(4acpy) 2 have been thoroughly reexamined on both powder and well-oriented single crystal samples. This azido-bridged cobalt compound of (4, 4) layer shows a weak-ferromagnetic state below T C = 11.2 K. The magnetic axes were determined to be along the crystallographic a*, b, and c axes for the monoclinic space group P2 1/c. The easy axis lies along the b-axis, the canting is along the a*-axis, and the hard axis is along the c-axis. Strong anisotropy due to the oriented moments in the ordered state and/or the single-ion anisotropy of Co (2+) exists in the whole temperature range from 2 to 300 K. Below T C, very big spontaneous magnetization was observed and was attributed to the very big canting angle (15 degrees at 2 K). A possible spin configuration was then proposed to explain the experimental results. The origin of the big spin canting was discussed, and a weak-ferromagnetic approach toward molecular magnets with big spontaneous magnetization was proposed accordingly.