3.3-Dichloro-N-p-methoxyphenyl-4-(2-phenylstryl)-2-azetidinone (C22H15Cl2NO2) was studied by X-Ray analysis, which indicated a monoclinic space group, P2(1)/c, with a = 9.619(5), b = 13.879(4), c = 14.161(5)Angstrom, beta = 100. 16(3)degrees, V = 1860.8(13)Angstrom(3), Z = 4, D-c = 1.414 g cm(-3), mu(Mo K-a) = 0.366 mm(-1) and F-000 = 816. The structure was solved by direct methods and refined to R = 0.041 for 4026 reflections [I > 2sigma(I). The beta-lactam ring (2-azetidinone) has antimicrobial affects. The substituents of the methoxyphenyl and phenyl substituents do not change the activity property of the betalactam ring, and the activity properties depend on the planarity of the beta-lactam ring.