Cyclopeptides are promising candidates for developing bioactive molecules and drugs, but due to the scarcity of efficient cyclization strategies for natural peptides, the development of novel cyclopeptides remains challenging. Here, the authors report the development of a variety of macrocyclic peptides featuring (thio)urea bridges through site-selective Lys-Lys crosslinking of native peptides, employing N,N′-carbonyldiimidazole (CDI) or N,N′- thiocarbonyldiimidazole (TCDI) as bridging reagents.