We studied the knockdown activity and lethal toxicity of 6 essential oil compounds—methyl salicylate, linalool, 2-phenethyl alcohol, eugenol, β-citronellol, and trans-cinnamaldehyde—as fumigants against adult female Culex pipiens pallens in the laboratory. Of the 6 products tested, trans-cinnamaldehyde was the most toxic (LC₅₀  =  0.26 µl/l air, 24 h) with a slow knockdown time (KT₉₅  =  176.5 min at 0.5 µl/l air). Methyl salicylate displayed a lower toxicity (LC₅₀  =  1.17 µl/l air, 24 h) but the fastest knockdown activity (KT₉₅  =  16.8 min) at the sublethal concentration 0.5 µl/l air. Furthermore, the binary mixture of methyl salicylate and trans-cinnamaldehyde exhibited a combined effect of fast knockdown activity and high toxicity against Cx. p. pallens adults, showing potential for development as natural fumigants for mosquito control.