During mitotic exit in metazoans, the properly segregated chromosome mass is typically enclosed by the newly formed nuclear envelope to form a single nucleus in each daughter cell. On the other hand, mis-segregated chromosomes that lag behind can also undergo nuclear envelope assembly, leading to the formation of atypical nuclear structures such as micronuclei. Micronuclei are commonly observed in cancer and are known to cause extensive genome alterations such as chromothripsis. Recent studies highlight that micronuclei frequently exhibit fragile nuclear envelopes and undergo defective nuclear envelope assembly, which are linked to numerous adverse consequences, including abnormal DNA replication, DNA damage, transcriptional defects, and proinflammatory immune responses. In this chapter, I describe methods to examine nuclear envelope assembly on micronuclei during chromosome mis-segregation.