The crystal and molecular structures of 1-Methyl-2-Isopropyl-5-Nitroimidazole (A) and 1-Methyl-2(Thiophenyl)-Methyl-5-Nitroimidazole (B) derivatives were determined by X-ray diffraction methods. The compound A, C7H11N3O2 crystallises in the monoclinic space group P2(1)/c with a = 9.9582(2) Angstrom, b = 6.5240(4) Angstrom, c = 13.5560(3) Angstrom, beta = 99.8930(17)degrees, V = 867.6(5) Angstrom(3), Z = 4, D-calc = 1.295 Mg/m(3), mu = 0.813 mm(-1), F-000 = 360, CuK alpha = 1.5406 Angstrom and R = 0.09. The five membered ring with two nitrogen atoms is planar. Layering is observed down a and b axes. The compound B, C11H11N3O2S crystallises in the triclinic space group P (1) over bar with a = 6.270(10) Angstrom, b = 27.874(12) Angstrom, c = 12.960(3) Angstrom, alpha = 90 degrees, beta = 89.90 degrees, gamma = 90 degrees, V = 2266(35) Angstrom(3), Z = 8, D-calc = 1.461 Mg/m(3), mu = 2.504 mm(-1), F-000 = 1040, CuK alpha = 1.5406 Angstrom and R = 0.11.