永生细胞系，是指一组在多细胞生命中的细胞群，因为基因突变，已经逃避了正常的细胞衰老，而是可以继续进行分裂，甚至无限无止境地繁殖，细胞可以在体外长时间生长。
永生细胞系，可以来自自然发生的突变，例如癌细胞。也可以出于实验目的有意诱导。 永生细胞系是研究多细胞生物的生物化学和细胞生物学的非常重要的工具。
永生细胞系也用于生物技术。值得留意的是，干细胞虽然可以不断分裂繁殖，但不属永生细胞系。
目前著名的永生细胞系包括海拉细胞。[1][2][3][4][5][6]
Skloot, Rebecca. Henrietta's Dance. Johns Hopkins Magazine. [5 April 2021]. （原始内容存档于2021-11-30）. Isolation from a naturally occurring cancer. This is the original method for generating an immortalised cell line. Major examples include human HeLa, the line is derived from cervical cancer cells taken on February 8, 1951 from Henrietta Lacks, a 31-year-old African-American mother of five, who died of cancer on October 4, 1951.
Henle W, Henle G. Epidemiologic aspects of Epstein-Barr virus (EBV)-associated diseases. Annals of the New York Academy of Sciences. 1980, 354: 326–31. PMID 6261650. S2CID 30025994. doi:10.1111/j.1749-6632.1980.tb27975.x. Introduction of a viral gene that partially deregulates the cell cycle (e.g., the adenovirus type 5 E1 gene was used to immortalise the HEK 293 cell line; the Epstein-Barr virus can immortalise B lymphocytes by infection
