Starting with γ-butyrolactone, 4-amino-3-(3-hydroxypropyl)-1H-1,2,4-triazole-5-(4H) thione I was prepared, and cyclization of it with 4-phenylbromoacetophenone gave 6-(4-biphenylyl)-3-(3-hydroxypropyl)-7H-1,2,4-triazolo[3,4-b][1,3,4]thiadiazine Ⅱ. The structures of Ⅰ and Ⅱ were determined by elemental analyses, IR, 1H NMR, 13C NMR, and X-ray diffraction. Crystal data for Ⅰ:C5H10N4OS, Mr = 174.23, monoclinic system, space group P21/c, a = 8.4568(6), b = 22.8905(16), c =9.2625(6)(A), β = 114.172(1)°, V= 1635.82(19)(A)3, F(000) = 736, Z = 8, Dc = 1.415 g/cm3, λ = 0.71073(A), μ = 0.346 mm-1 and the final R = 0.0603 for 2870 unique reflections with 1993 observed ones (I ＞2σ(I)). Crystal data for Ⅱ: C19H18N4OS, Mr = 350.43, monoclinic system, space group P21/c, a =6.7481(7), b = 8.2647(8), c = 30.075(3) (A), β = 94.445(2)°, V= 1672.3(3)(A)3, F(000) = 736, Z = 4, Dc =1.392 g/cm3, λ = 0.71073 (A), μ = 0.209 mm-1 and the final R = 0.0667 for 3000 unique reflections with 2534 observed ones (I ＞ 2σ(I)). In the crystal of compound Ⅱ, the five-membered triazole ring and two benzene rings are coplanar, while the six-membered thiadiazine ring is slightly distorted, with an r.m.s deviation of 0.227(1)(A). Some hydrogen bonding interactions are observed and π-π stacking interactions between adjacent molecules are found in the packing diagrams of the two compounds.