Two Sideritis species afforded eleven kaurene and one beyerene diterpenes. Structures of the compounds from Sidcritis sipylca were elucidated as linearol (1), 7-epicandicandiol (2), sideridiol (3), siderol (4), isolinearol (5), isosidol (6) and epoxyisolinearol (7). Linearol was treated with m-chloroperbenzoic to afford its analogues ent-3beta,7alpha,17-triliydroxy-18-acetoxykaur-15-ene (1a) and ent-7alpha,17,18-trihydroxy-3beta-acetoxykaur-15-ene (1b) as new compounds. From the second species, Sideritis dichotoma, the kaurenes sideridiol (3) siderol (4), ent-7alpha,18-dihydroxy-15beta,16beta-epoxykaurane (8), ent-7alpha-acetoxy,18-hydroxy-15beta,16beta-epoxykaurane (9), ent-7alpha-acetoxy-15,18-dihydroxy-kaur-16-ene (10), ent-7alpha,15,18-trihydroxykaur-16-ene (11) and the beyerene ent-7alpha,18-dilhdroxybeyer-15-ene (12) were isolated. Structural elucidation is based on NMR techniques and mass spectrometer analyses.