Background and Purpose: The advanced glycation end products (AGEs) participate in the pathogenesis of diabetic nephropathy (DN) by promoting renal inflammation and injury. L-carnosine acts as a quencher of the AGE precursors reactive carbonyl species (RCS), but is rapidly inactivated by carnosinase. In this study, we evaluated the effect of FL-926-16, a carnosinase-resistant and bioavailable carnosine derivative, on the onset and progression of DN in db/db mice. Experimental Approach: Adult male db/db mice and coeval db/m controls were left untreated or treated with FL-926-16 (30 mg·kg−1 body weight) from weeks 6 to 20 (prevention protocol) or from weeks 20 to 34 (regression protocol). Key Results: In the prevention protocol, FL-926-16 significantly attenuated increases in creatinine (−80%), albuminuria (−77%), proteinuria (−75%), mean glomerular area (−34%), fractional (−40%) and mean (−42%) mesangial area in db/db mice. This protective effect was associated with a reduction in glomerular matrix protein expression and cell apoptosis, circulating and tissue oxidative and carbonyl stress, and renal inflammatory markers, including the NLRP3 inflammasome. In the regression protocol, the progression of DN was completely blocked, although not reversed, by FL-926-16. In cultured mesangial cells, FL-926-16 prevented NLRP3 expression induced by RCS but not by the AGE Nε-carboxymethyllysine. Conclusion and Implications: FL-926-16 is effective at preventing the onset of DN and halting its progression in db/db mice by quenching RCS, thereby reducing the accumulation of their protein adducts and the consequent inflammatory response. In a future perspective, this novel compound may represent a promising AGE-reducing approach for DN therapy.