A novel series of acylides, 3-O-carbamoyl derivatives of 6,11-di-O-methylerythromycin A, were synthesized and evaluated for their antibacterial activity. These compounds have significant antibacterial activity against gram-positive pathogens, including erythromycin-resistant but methicillin-susceptible Staphylococcus aureus, erythromycin-resistant and methicillin-resistant S. aureus, erythromycin-resistant Streptococcus pneumoniae, and gram-negative pathogens, such as Haemophilus influenzae. Among the derivatives tested, compounds 4p, 4r, 4w, 4x and 4z were found to have potent activity against most susceptible and resistant bacteria. Compound 4p exhibited excellent antibacterial activity in comparison to the others.