A series of Lycopodium alkaloids, namely lycosquarosine A (1), acetylaposerratinine (2), huperzine A (3), huperzine B (4), 8α-hydrophlemariurine B (5), and huperzinine (6), has been isolated from Vietnamese Huperzia squarrosa. Among them, lycosquarosine A (1) is the new metabolite of the natural source. Lycosquarosine A completely inhibited AChE activity in a dose dependent manner with an IC50 value of 54.3 μg/mL, while acetylaposerratinine (2) showed stronger inhibitory activity than 1 with an IC50 value of 15.2 µg/mL. This result indicates that these alkaloids may be a potent source of AChE inhibitors.