Abstract: With the progression of research on extrachromosomal DNA (ecDNA), it has been shown that ecDNA exists mainly in tumor cells and plays a crucial role in tumor heterogeneity and drug resistance. ecDNA is observed in several cancer types, but rarely in normal cells. Due to their strong oncogene amplification and dynamic alteration capabilities, patients with ecDNA-containing tumor cells often have negative clinical prognoses. Research has confirmed the presence of ecDNA in the cancer cells of patients with small cell lung cancer (SCLC). This review provides a comprehensive summary of the formation mechanism of ecDNA, the processes through which it is amplified in cancer cells, the mechanisms through which ecDNA promotes tumor growth, recurrence, and metastasis, and its relationship with high drug resistance in SCLC. Finally, we generalize the treatment direction for ecDNA-enriched SCLCs, thereby guiding future research.