We attempted to identify the difference in diuretic properties between tolvaptan (TLV) and furosemide (FUR) in congestive heart failure (CHF) patients with loop diuretic resistance and renal impairment. We investigated 81 CHF patients with loop diuretic treatment and renal impairment included in t he Kanagawa Aquaresis Investigators Trial of Tolvaptan on Heart Failure Patients with Renal Impairment (K-STAR). Predictive baseline factors and their changes during treatment periods were analyzed for correlation with percentage change in urine volume (%ΔUV) after additive introduction of TLV or increasing doses of FUR. Higher urine osmolality at baseline (β = 0.355; p = 0.033) in the TLV group and a lower ratio of blood urea nitrogen to serum creatinine (BUN/Cr, β = − 0.405; p = 0.020) in the FUR group were predictive of higher %ΔUV. Higher Δfree-water clearance (β = 0.667; p < 0.0001) in the TLV group, and higher %ΔBUN/Cr (β = 0.344; p = 0.030), higher %Δurine sodium concentration (β = 0.337; p = 0.037), and lower %Δstroke volume (β = − 0.390; p = 0.017) in the FUR group were correlated with %ΔUV. In conclusion, baseline urine osmolality and change in free-water clearance with additive introduction of TLV and a changing ratio of BUN/Cr with increasing doses of FUR were identified as key clinical parameters related to diuretic response.