Novel 4″-O-benzimidazolyl clarithromycin derivatives were designed, synthesized and evaluated for their in vitro antibacterial activities. These benzimidazolyl derivatives exhibited excellent activity against erythromycin-susceptible strains better than the references, and some of them showed greatly improved activity against erythromycin-resistant strains. Compounds 16 and 17, which have the terminal 2-(4-methylphenyl)benzimidazolyl and 2-(2-methoxyphenyl)benzimidazolyl groups on the C-4″ bishydrazide side chains, were the most active against erythromycin-resistant Staphylococcus pneumoniae expressing the erm gene and the mef gene. In addition, compound 17 exhibited the highest activity against erythromycin-susceptible S. pneumoniae ATCC49619 and Staphylococcus aureus ATCC25923 as well. It is worth noting that the 4″-O-(2-aryl)benzimidazolyl derivatives show higher activity against erythromycin-susceptible and erythromycin-resistant strains than the 4″-O-(2-alkyl)benzimidazolyl derivatives.