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Herein we report a feasible study concerning the synthesis and the in vitro antimicrobial activity of some new homodrimane sesquiterpenoids with a benzimidazole unit. Based on some homodrimane carboxylic acids, on their acyl chlorides and intermediate monoamides, a series of seven <i>N</i>-homodrimenoyl-2-amino-1,3-benzimidazoles and 2-homodrimenyl-1,3-benzimidazoles was synthesized. The syntheses involved the decarboxylative cyclization and condensation of the said acids or acyl chlorides with <i>o</i>-phenylendiamine and 2-aminobenzimidazole, as well as the <i>p</i>-TsOH-mediated cyclodehydration of the said monoacylamides. The structures of the synthesized compounds have been fully confirmed, including by the X-ray diffraction. Their biological activities were evaluated on five species of fungi (<i>Aspergillus niger</i>, <i>Fusarium solani</i>, <i>Penicillium chrysogenum</i>, <i>P. frequentans</i>, and <i>Alternaria alternata</i>) and two strains of bacteria (<i>Bacillus</i> sp. and <i>Pseudomonas aeruginosa</i>). Compounds <b>7</b> and <b>20</b> showed higher antifungal (MIC = 0.064 and 0.05 μg/mL) and antibacterial (MIC = 0.05 and 0.032 μg/mL) activities compared to those of the standards: caspofungin (MIC = 0.32 μg/mL) and kanamycin (MIC = 2.0 μg/mL), and compounds <b>4</b>, <b>10</b>, <b>14</b>, and <b>19</b> had moderate activities.