Maternal obesity increases risk of chronic kidney disease in the mother. In this study, we aimed to determine if preconception weight loss with diet modification improves kidney outcomes in late gestation, over diet change in pregnancy. Methods:C57BL/6 female mice were fed either a high-fat-diet (HFD) or chow diet for 8 weeks. To induce pre-pregnancy weight loss, 8 HFD-fed dams were switched to chow diet pre-pregnancy 4 weeks prior to matting. This was compared to a group of 8 HFD-fed dams who underwent ‘diet switched’ to chow diet after conception. 8 dams continued on chow as controls and HFD for comparison. Maternal body weight and glucose tolerance were observed prior to collection of blood and kidney samples, either prior to pregnancy or during late gestation. Serum creatinine, urinary creatinine and albumin were measured. Gene expression within kidney tissue was measured using real-time PCR, and protein expression measured by immunohistochemistry. Results: HFD-fed dams had increased renal expression of Insulin receptor and Fatty acid synthase (both P<0.05) pre-pregnancy and higher Urine Albumin: creatinine ratios (UACR) compared to control (P<0.01). In the group with ‘diet switch’ after conception, though gestational weight gain was lower than the other 3 groups (P<0.05) and body weight similar to the control group (P<0.01), glucose tolerance was impaired compared to control (P<0.05), and kidney tissue had increased expression of metabolic and oxidative stress markers, (8-OHDG P<0.0001, FAS, P<0.05) compared to mice who underwent preconception weight loss. Preconception renal fibrosis markers (Collagen IV, Fibronectin) and UACR were significantly reduced in mice who achieved preconception weight loss compared to HFD fed mice (P<0.05). These effects were sustained in pregnancy. Conclusion: Preconception weight loss has benefits on renal health in the preconception period and in pregnancy overweight optimisation in pregnancy alone.