Although n-3 polyunsaturated fatty acids (PUFAs) exhibit biological activity in many inflammatory diseases, their renoprotective effects against diabetic nephropathy (DN) have been controversial. Here, fat-1 transgenic mice were used to investigate the effects of n-3 PUFA5 on streptozocin (STZ)-induced DN. Fat-1 mice exhibited increased renal n-3 PUFAs and n-3 PUFA-derived lipid mediators, compared to wild type (WT) mice. Endogenous n-3 PUFAs protected STZ-treated fat-1 mice against hyperglycemia-induced renal dysfunction, as reflected by significant decreases in kidney/body weight ratio, urinary protein, blood urea nitrogen levels and creatinine clearance. In addition, endogenous n-3 PUFAs significantly ameliorated hyperglycemia-induced renal damage by modulating E-cadhein expression. It was also found that DN-induced NLRP3 inflammasome activation was attenuated by endogenous n-3 PUFA5 in STZ-treated fat-1 mice. Our findings suggest that endogenous n-3 PUFAs ameliorate DN potentially through the: (i) formation of n-3 lipid mediators, (ii) induction of E-cadherin expression and (iii) inhibition of NLRP3 inflammasome.