*Purpose: We often experience the incompatibility in size between the kidney graft and recipient in living-donor kidney transplantation. This study evaluated the effect of the donor kidney to recipient body weight ratio (Kw/Rw) on long-term graft function and survival.

*Methods: This study included 932 living-donor kidney transplant recipients from January 2000 to December 2016 in our institute. According to the Kw/Rw (in g/kg), patients were divided into 3 groups: Lower group (n = 294), Middle group (n = 374), and Higher group (n = 264). We investigated retrospectively the association between Kw/Rw and long-term graft survival and renal function. Kidney grafts were weighed by the surgeon before preparation in the operating room.

*Results: The mean Kw/Rw was 2.2±0.3 g/kg (1.2-2.5) in Lower group, 3.0±0.3 g/kg (2.6-3.5) in Middle group and 4.4±0.8 g/kg (3.6-8.3) in Higher group. As the Kw/Rw was lower, the proportion of male recipient was higher and the proportion of male donor was lower. The mean eGFR (ml/min/1.73m²) between 2weeks and 10years was 44.6±0.9 in Lower group, 49.1±1.1 in Middle group and 51.9±1.5 in Higher group. In all groups, the value of eGFR increased until 2 years after the transplantation, remained stable until 5 years, and decreased since then. The decline rate of eGFR (ml/min/1.73m²/year) was -0.34, -0.54, and -0.94, respectively. The eGFR in 10 years after transplantation was 42.9±14.7 in Lower group, 46.9±15.1 in Middle group and 48.8±18.0 in Higher group (p = 0.066). The 10-year graft survival rates did not show significant difference among three groups (p = 0.229). However, Lower group had lower 10-year graft survival rates (80.8%) than Middle and Higher group (86.3 and 87.3, respectively). The incidence of antibody mediated rejection and T-cell mediated rejection did not show significant difference.

*Conclusions: Lower Kw/Rw was associated with poor graft function and graft survival. Our data suggests that recording Kw/Rw may help to improve late clinical outcome and may be relevant in the context or poor long-term graft survival.

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