Animal studies suggest that the kidney is involved in the elimination of recombinant human granulocyte colony-stimulating factor (rhG-CSF), which is used for patients with neutropenia during cancer chemotherapy. Since anticancer drugs induce nephrotoxicity, it is important to clarify the role of the kidney in the pharmacokinetics of rhG-CSF in cancer patients. Our study was designed to evaluate the relationship between the pharmacokinetics of rhG-CSF and renal function in lung cancer patients compared to the absolute neutrophil count (ANC). The pharmacokinetic studies were conducted with 25 lung cancer patients. Following chemotherapy using platinum-based compounds, a bolus 5 µg of rhG-CSF/kg of body weight was intravenously injected from the first day of leukopenia or neutropenia. Pharmacokinetic parameters were estimated by fitting the concentration in serum-time data to a two-compartment model according to the population pharmacokinetics and the Bayesian method. Creatinine clearance (CL_CR) was predicted by the Cockcroft-Gault formula. rhG-CSF clearance (CL_G-CSF) correlated significantly with the ANC (r = 0.613; P < 0.001) and CL_CR (r = 0.632; P < 0.001). Multiple linear regression analysis showed that the combination of the ANC and CL_CR accounted for 57.4% of the variation of CL_G-CSF. In patients with an ANC of <1,000/µl, CL_CR accounted for 72.9% of the variation of CL_G-CSF (P < 0.001). Our findings suggest that renal function and neutrophil counts correlate with CL_G-CSF and that the role of renal function in eliminating rhG-CSF is important in lung cancer patients with neutropenia.