A five-membered phosphoroheterocycle, 5, 5-dimethyl-2-(4 -methoxy)phenyl-1, 3, 2-thiazaphospholidine-4-thione 2-sulfide, has been prepared by the reaction of Lawessons reagent (LR) with -hydroxyl isobutyronitrile, and its crystal structure was determined by X-ray diffraction method. The title compound (C11H14NOPS3) is triclinic with space group P , a= 6.8418 (9), b= 10.5467 (1), c= 11.5670 (2)? = 114.851 (2),β= 100.291 (2),γ= 91.390 (3)? V= 740.7 (2) 3, Z= 2, Dc= 1.360 g/cm3, λ= 0.71073 ? μ(MoK?= 0.59 mm-1, F(000)= 316. The Structure was refined to R= 0.0476, wR= 0.1272 for 2549 unique reflections with I >2σ(I). It contains a phenyl ring and a 5-membered phosphoroheterocycle with the dihedral angle of 87.06 (9)? The five atoms (P (1), N (1), C (1), C (2) and S (2)) of the heterocycle are nearly coplanar. In view of the unit cell it can be concluded that there exists an intermolecular hydrogen bond in the form of Sa┈HN (a: X, Y+1,Z+1). The existence of dpлbond between P (1) and N (1) was found as well as unsaturated property of N (1)C (1) moiety. 5-dimethyl-2- (4-methyloxy) phenyl-1, 3, 2-thiazaphospholidine-4-thione 2-sulfide, has been prepared by the reaction of Lawessons reagent (LR) with - hydroxyl isobutyronitrile, and its crystal structure was determined by X-ray diffraction method. The title compound (C11H14NOPS3) is triclinic with space group P, a = 6.8418 (9), b = 10.5467 (1), c = = 114.851 (2), β = 100.291 (2), γ = 91.390 (3)? V = 740.7 (2) 3, Z = 2, Dc = 1.360 g / cm3 and? = 0.71073? -1, F (000) = 316. The Structure was refined to R = 0.0476, wR = 0.1272 for 2549 unique reflections with I> 2σ (I). It contains a phenyl ring and a 5-membered phosphoroheterocycle with the dihedral angle of 87.06 (9)? The five atoms (P (1), N (1), C (1), C (2) and S (2)) of the heterocycles are nearly coplanar. there is an intermolecular hydrogen bond in the form of Sa┈HN (a: X, Y + 1, Z + 1). The existence of dpлbond between P (1) and N (1) was found as well as unsaturated property of N (1) C (1) moiety.