The terpenoids are one of the secondary metabolities in Pinus species and functioned the protection them from insects or/and fungus etc. Since Pinus koraiensis has not any damage by Pine needle gall midge but Pinus densiflora has great injury by them in South Korea. It may great helf to find these reasons to analize their monoterpenenoids and to compare the seasonal variation of their amounts. Terpenoids were analized by GC, GC/MS. Some biogenetic analysis of terpenoids also was elucidated. The seasonal variation of terpenoid was distinguished at March and August and/or September. Most of major component of monoterpenes were increased or decreased in these periods in Pinus koraiensis. Especially 3-carene was showed significant variation between the period of physiological activity and the period of domain. The effect of infection by Pine needle gall midge was significant in Pinus densiflora for amount of monoterpene during the period of infection. The components of p-menthane series between Pinus densiflora and Pinus koraiensis was recognized a significant difference during the experiment. Biogenetic cooccurrance of pmenthane series also was recognized between 3-carene and terpinolene in Pinus koraiensis.