The function of COX18 (cytochrome c oxidase assembly factor COX18, ENSG00000163626) is as follows. Mitochondrial membrane insertase required for the translocation of the C-terminus of cytochrome c oxidase subunit II (MT- CO2/COX2) across the mitochondrial inner membrane. Plays a role in MT- CO2/COX2 maturation following the COX20-mediated stabilization of newly synthesized MT-CO2/COX2 protein and before the action of the metallochaperones SCO1/2. Essential for the assembly and stability of the mitochondrial respiratory chain complex IV (also known as cytochrome c oxidase). {ECO:0000269|PubMed:16911509, ECO:0000269|PubMed:28330871}.