Objective: To study prognostic effects of nadirs of neutrophils and lymphocytes during radical (chemo)radiotherapy for cervical cancer. Methods: Patients with International Federation of Gynecology and Obstetrics (FIGO) IB1-IVA cervical cancer from January 2015 through December 2019 were retrospectively analyzed. All patients were treated with radical (chemo)radiotherapy and had available baseline and weekly complete blood counts with differentials before and during treatment. Results: A total of 107 patients were eligible. Receiver operating characteristic (ROC) curve determined the cutoff values predicting overall survival (OS) of nadirs of absolute neutrophil count (ANC) and absolute lymphocyte count (ALC) during treatment were 2.62 \times 10{}^9/L and 0.2 \times 10{}^9/L, respectively. Compared with ANC nadir \le2.62 \times 10{}^9/L (N = 94), patients with ANC nadir >2.62 \times 10{}^9/L (N = 13) had lower 2-year OS rate (51.9% vs 88.7%, p = 0.01) and lower 2-year progression-free survival (PFS) rate (52.7% vs 80.8%, p = 0.003); compared with ALC nadir >0.2 \times 10{}^9/L (N = 65), patients with ALC nadir \le0.2 \times 10{}^9/L (N = 42) had lower 2-year OS rate (74.7% vs 90.0%, p = 0.004) and lower 2-year PFS rate (67.8% vs 83.3%, p = 0.038). Multivariate COX analysis showed that ANC nadir (>2.62 vs \le2.62 \times 10{}^9/L) (hazard ratio (HR) 4.729, 95% confidence interval (CI) 1.355–16.505, p = 0.015), ALC nadir (\le0.2 vs >0.2 \times 10{}^9/L) (HR 4.463, 95% CI 1.616–12.321, p = 0.004) were associated with OS. Conclusions: Peripheral ANC nadir and ALC nadir during radical (chemo)radiotherapy have different prognostic effects in predicting treatment outcome. ANC and ALC nadir during radical (chemo)radiotherapy may serve as a guide to treatment of cervical cancer.