Some pyridazine derivatives carrying urea, thiourea, and sulfonamide groups were synthesized and evaluated for their antimicrobial activity against gram-positive and gram-negative bacteria, and fungi by using broth microdilution. The structures of these new compounds were confirmed by (1)H-NMR, mass spectrum, and elemental analysis. The synthesized compounds exhibited generally promising inhibitory activity against S. aureus (MIC ranging from 2 to 4 mu g/mL) and E. coli (MIC ranging from 4 to 16 mu g/mL). Moreover, all compounds showed antifungal activity against both C. albicans and C. parapsilosis, with a MIC value of 8 mu g/mL.