The role of terpenes on flammability is not clearly determined, especially for species used in wildland-urban interfaces (WUI) where the fire risk is high. This work aims at checking if the leaf flammability of different WUI species (Pinus halepensis, Cupressus sempervirens, C. leylandii, and C. arizonica) varied across seasons possibly highlighting the role of leaf moisture content (FMC) and terpene content (investigated at three levels: total, family and compounds). All year round, P. halepensis presented the highest flammability related to high content in sesquiterpenes, mostly caryophyllene and α-humulene, and low FMC in contrast to C. arizonica. Species presented different seasonal flammability and terpene patterns. Diterpene totarol, sesquiterpene germacrene, and monoterpene myrcene increased flammability (in C. sempervirens, C. arizonica, and P. halepensis, respectively) while monoterpene α-pinene (in P. halepensis) and several other diterpene compounds, especially manool oxyde-13-epi, decreased it (in C. leylandii). Terpene compounds linked to flammability seasonally varied only in C. leylandii, the species showing the highest diversity of compounds. FMC did not affect flammability, except time-to-ignition in C. sempervirens. Regardless of season, the highly flammable species should be avoided close to housing, especially when they form horizontal fuel continuity (as in ornamental hedge) that can easily propagate the fire.