Ten new azo Schiff bases 5a-h and 7a-b were prepared in excellent yields via the condensation of different aromatic amines and a new azoaldehyde, 2-hydroxy-3- methoxy-5-(4-methoxyphenylazo)benzaldehyde (4) by two different methods. All new compounds were tested against five microorganisms: Staphylococcus aureus (Gram positive and methicillin resistant), Bacillus subtilis (Gram positive), Kelebsiella pneumonia, Pseudomonas aeruginosa and Escherichia coli (all Gram negative). Compounds 4, 5a, 5c, 5d and 5g were moderately active against Staphylococcus aureus and Bacillus subtilis. Compound 7b was highly active against Bacillus subtilis and moderately active against Staphylococcus aureus. Other compounds were inactive against these strains of bacteria. The antifungal activities of these compounds were also tested against eight different fungal species. None of them were active against the fungi species tested.