The 2-phenyl-2-(1-hydroxyiminoethyl)-1,2,3,4-tetrahydroquinazoline (HL) and its Ni-II complex have been prepared and characterized by spectral method (FT-IR, NMR (C-13 and H-1), UV-vis.), elemental analysis, magnetic susceptibility and thermal analysis (TG, DTA) techniques. The crystal structures of HL and Ni-II complex were also determined by the single crystal X-ray diffraction. The HL and Ni-II complex crystallizes in the monoclinic and triclinic, space groups P2(1)/c and P (1) over bar, respectively The complex was occurred by the elimination of 1 mole of 2-aminobenzylamine from the 2 moles of the HL after the ring opening reaction by the Ni-II attack. Crystallographic study reveal that Ni-II atom has a square planer geometry being coordinated by four nitrogen atoms of HL. Two thermal processes of the HL and Ni-II complex can occur in TG and DTA curves.