Background/Aim: This study aimed to investigate the effects of the combination of alkalization therapy (an alkaline diet and bicarbonate therapy) and intravenous vitamin C treatment on chemotherapy outcomes in patients with small-cell lung cancer (SCLC) (study registration: UMIN000043056). Patients and Methods: Twelve patients with SCLC in the intervention group (receiving both alkalization therapy and vitamin C treatment together with chemotherapy) were retrospectively compared to 15 patients with SCLC in the control group (receiving chemotherapy only). Results: The mean urine pH of the intervention group was significantly higher than that of the control group (7.32±0.45 vs. 6.44±0.74, respectively; p<0.005). The median overall survival for the intervention group was 44.2 months (95% confidence interval=22.0−not reached), as compared with 17.7 months for the control group (95% confidence intervaI=13.5−not reached; p<0.05). Conclusion: The combination of alkalization therapy and intravenous vitamin C treatment may be associated with favorable outcomes in patients with SCLC receiving chemotherapy.