A new lycopodane-type Lycopodium alkaloid, 6-hydroxy-5,15-oxide-lycopodane (1), and seven known alkaloids were isolated from the whole plants of Huperzia serrata. Their structures were elucidated by means of spectroscopic methods. 12-Deoxyhuperzine O (2) was reported as a naturally occurring alkaloid for the first time, and showed an antagonist effect on the N-methyl-d-aspartate receptor with an IC50 value of 0.92M.