Curative cancer treatment can significantly impair reproductive function. In females, DNA-damaging cancer treatments deplete the ovarian reserve by destroying primordial follicles, potentially causing premature ovarian failure, ovarian endocrine failure, and consequently infertility. Previous mouse studies have shown that elimination of the potent pro-apoptotic protein, PUMA, protects primordial follicles from γ-irradiation-induced apoptosis1. This study aimed to determine the role of PUMA in mediating DNA damaging chemotherapy-induced follicle death. Postnatal day (PN) 50 female Puma-/-or wild-type (WT) mice received intraperitoneal injection of saline, cisplatin (5mg/kg), or cyclophosphamide (300mg/kg) (N=5/group). Ovaries were harvested 5 days after treatment and follicles enumerated stereologically. Saline-treated WT females contained 4982±760 (mean±SEM) primordial follicles per animal. Treatment with cisplatin or cyclophosphamide caused a dramatic reduction in this number, with only 27% of primordial follicles surviving following cisplatin treatment (control WT: 4982±760 vs cisplatin WT: 1365±308, p<0.05), and only 4% surviving after cyclophosphamide (control WT: 4982±760 vs cyclophosphamide WT: 212±79, p<0.05). In marked contrast, primordial follicle numbers were completely preserved in cyclophosphamide-treated Puma-/- females compared with saline-treated Puma-/- controls (control Puma-/-: 6294±955 vs cyclophosphamide Puma-/-: 7251±995). A protective effect of PUMA loss was also observed for cisplatin (control Puma-/-: 6294±955 vs cisplatin Puma-/-: 5035±574, p<0.05; 80% survival). A second cohort was treated similarly, then bred with proven males. Preliminary results of the fertility study show that cyclophosphamide-treated WT females have a shortened fertile lifespan (-71.5±27.4 days, p=0.028) and fewer litters (-1.37±0.38 litters, p=0.006). This was ameliorated in cyclophosphamide-treated Puma-/- females (age at last litter; control Puma-/-: 282.5±20 days vs cyclophosphamide Puma-/-: 320±7.6 days). Overall, this study demonstrates that PUMA plays an essential role in mediating oocyte death induced by cyclophosphamide or cisplatin in mice, and its elimination preserves fertility and the fertile lifespan. Inhibition of apoptosis presents a promising strategy for protection of the ovarian reserve during chemotherapy in women.