The whole plants of Ajuga lupulina afforded five compounds, including three new clerodane diterpenes, lupulins A-C (1-3), whose structures were elucidated by spectral methods. Among these compounds, lupulins A (1) and B (2) as well as the acid hydrolysate (5) of lupulin D (4) showed antibacterial activities against Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli.