Limited data assessing the clinical significance of post-left ventricular assist device (LVAD) in renal function are available. We aimed to investigate the impact of changes in renal function after LVAD implantation on subsequent long-term outcomes. We followed 184 patients with HeartMate II LVADs implanted between May 2008 and November 2014. Serial assessment of renal function, was performed at baseline and at day 1, day 7, 1 month, 3 months, 6 months, 1 year, and 2 years after implantation. Effects of 1-month GFR and changes in GFR from baseline to 1 month on long-term mortality and hospital re-admission were evaluated. There were 30 patients with GFR <45 (low), 44 with GFR 45 to 59 (intermediate), and 110 with GFR ≥60 (normal) at baseline. Only patients with baseline GFR <45 experienced significant improvement in GFR after 2 years of follow-up (p = 0.012). At 1 month, a higher GFR category was significantly associated with a 31% reduction in mortality (hazard ratio [HR] 0.69, CI 0.49 to 0.98, p = 0.036), but not re-admission. Patients with baseline low and intermediate GFR who had no improvement in renal function category at 1 month experienced significantly greater risk of mortality (HR 1.95, CI 1.10 to 3.43, p = 0.022) and re-admission (HR 1.75, CI 1.07 to 2.84, p = 0.025), relative to patients whose GFR was normal at baseline and 1 month. In conclusion, renal function after LVAD implantation improves in patients with GFR <45. Change in renal function from baseline to 1 month after implantation is a powerful marker of long-term outcomes.