The title compound {[Ca(CHZ)(2)(H2O)](NTO)(2).3.5H(2)O}(n) was synthesized by using an aqueous solution of calcium 3-nitro-1,2,4-triazol-5-onate and carbohydrazide (CHZ, NH2NHCONHNH2). Its molecular structure was determined by X-ray diffraction and its crystals have monoclinic form, with space group C2/c, where a = 2.4483(4) nm. b = 1.2581(2) nm, c = 1.6269(3) nn, beta = 121.168(12)degrees, V = 4.2879(13) nm(3), Z = 8, d(c) = 1.727 g(.)cm(-3), mu (Mo K-alpha) = 3.9 cm(-1), M = 557.47, F(000) = 2312. The coordination polyhedron is a tricapped trigonal prism in a tetradecahedron with a coordination number of nine. The whole molecule has many long chains formed through the carbohydrazide bridges, and every long chain is unlimited along the c axis. The long chains are linked by hydrogen bonds to form the crystal structure.