5-allyl-2-hydroxy-3-methoxyazobenzene was prepared by the reaction of 4-allyl-2-methoxyfenol and benzenediazoniumchloride and crystallized from dimethylsulphoxide to yield crystals suitable for analysis. The molecular structure was identified by UV-VIS, IR, H-1-NMR, C-13-NMR and elemental analysis. The crystal structure of the title compound was determined as monoclinic by by single crystal X-Ray diffraction technique. The crystal parameters of this compound are as follows: monoclinic P 2 1/n, a=5.559(2) Angstrom, b=14.900(2) Angstrom, c=17.573(29) Angstrom, beta=98.58(1)degrees, V=1439.3(2) Angstrom(3), Z=2, Dx=0.610 g/cm(3), F(000)=284, lambda (MoK alpha)=0.71070 Angstrom, mu=0.041 mm(-1). The structure was solved by SHELXS-86 and refined by SHELXL-93. R=0.09 for 1107 observed reflections with I>2 sigma(I).