Clinical parameters with correlation to diuretic effects after initiation of sodium-glucose cotransporter-2 (SGLT2) inhibitors are unclear. We aimed to identify the factors associated with the diuretic effect observed following the initiation of SGLT2 inhibitors in patients with diabetes having an acute heart failure (HF). Fifty-six patients included were hospitalized for acute HF with diabetes and started on SGLT2 inhibitors. Changes in urine volume (ΔUV) and blood/urine laboratory parameters before and during the first 4 days of therapy were evaluated. Data were prospectively obtained under clinically stable conditions after initial HF treatment. UV increased following the initiation of SGLT2 inhibitors [UV at baseline (BL): 1383 ± 479 mL/day; ΔUV over 4 days: + 189 ± 358 mL/day]. Multivariate analysis revealed no association between BL-hemoglobin A1c or BL-estimated glomerular filtration rate and ΔUV. Conversely, higher BL-fasting plasma glucose (FPG) and higher BL-urine N-acetyl-β-D-glucosaminidase (NAG) were associated with a higher ΔUV. ΔUV was inversely associated with ΔFPG and ΔNAG, and positively associated with Δurinary sodium excretion. Elevated FPG and NAG both improved over 4 days of treatment. In conclusion, the diuretic effect of SGLT2 inhibitors was glycemia-dependent, and was associated with a reduction in elevated renal-tubular markers in hospitalized HF complicated with diabetes.