Developing new on-DNA reactions is paramount to the development of new encoded libraries in the pursuit of novel pharmaceutical lead compounds. Lactam-containing molecules have been shown to be effective in a wide range of therapeutic areas and therefore represent a promising target for further investigation by DNA-encoded library screening. In pursuit of this motif, we report a novel method for the introduction of lactam-containing structures onto a DNA headpiece through the Ugi four-center three-component reaction (4C-3CR). This novel method is successful in three different approaches to give unique on-DNA lactam structures: on-DNA aldehyde coupled with isonitriles and amino acids; on-DNA isonitrile coupled with aldehydes and amino acids; and on-DNA isonitrile coupled with amines and acid aldehydes.