Schiff bases N-(2-hydroxy-3-nitrobenzalidene)4-aminomorpholine (1) and N-(2-hydroxy- I -naphthylidene)4-aminomorpholine (2) were synthesized from the reaction of 4-aminomorpholine with 2-hydroxy-5-nitrobenzaldehyde and 2-hydroxy- 1 -naphthaldehyde. Compounds 1 and 2 were characterized by elemental analysis, IR, H-1 NMR, C-13 NMR and UV-Visible techniques. The UV-Visible spectra of the Schiff bases with OH group in ortho position to the imino group were studied in polar and nonpolar solvents in acidic and basic media. The structures of compounds 1 and 2 have been examined cyrstallographically, for two compounds exist as dominant form of enol-imines in both the solutions and solid state. The title compounds 1 and 2 crystallize in the monoclinic space group P2(1)/c and P2(1)/n with unit cell parameters: a=8.410(1) and 11.911(3), b=6.350(9) and 4.860(9), c=21.728(3) and 22.381(6) angstrom, beta=90.190(1) and 95.6(2)degrees, V=1160.6(3) and 1289.5(5) angstrom(3), D-x = 1.438 and 1.320 g cm(-3), respectively. The crystal structures were solved by direct methods and refined by full-matrix least squares. The antimicrobial activities of compounds 1 and 2 have also been studied. The antimicrobial activities of the ligands have been screened in vitro against the organisms Escherichia coli ATCC 11230, Staphylococcus aureus ATCC 6538, Klebsiella pneumoniae UC57, Micrococcus luteus La 297 1, Proteus vulgaris ATCC 8427, Pseudomonas aeruginosa ATCC 27853, Mycobacterium smegmatis CCM 2067, Bacillus cereus ATCC 7064, Listeria monocytogenes ATCC 15313, Candida albicans ATCC 1023 1, Kluyveromyces fragilis NRRL 2415, Rhodotorula rubra DSM 70403, Debaryomyces hansenii DSM 70238 and Hanseniaspora guilliennondii DSM 3432. 0 2004 Elsevier B.V. All rights reserved.