Theoretical and computational studies on the mechanisms of ligand exchange reaction (LER) and ligand coupling reaction (LCR) of hypervalent pentacoordinate Sb and tetracoordinate Te compounds were carried out. Contrary to the previous suggestion from experimentalists, the lone pair electrons of Te do not participate in LER. Also, LER of R₅Sb proceeds via a similar mechanism to that of R₄Te. As for the LCR of R₅Sb, the apical-equatorial coupling mechanism was suggested.