Leptoglossus occidentalis (Heidemann, 1910) and Cydalima perspectalis (Walker, 1859) are alien insect species which have invaded Turkey. Leptoglossus occidentalis was recorded for the first time in Istanbul (Turkey) in 2009 and Cydalima perspectalis was recorded there for the first time in 2011. We examined the distribution of these two invasive alien insect species, and their host plants, in Istanbul province of Turkey. Leptoglossus occidentalis was observed in Istanbul Province on Pinus nigra, Pinus pinea, Pinus radiata and Abies concolor. Cydalima perspectalis was recorded only on Buxus sempervirens and B. sempervirens cv 'aureavariegata' in Istanbul Province, and severe damage was inflicted on these cultivars.