Abstract Background and Aims Large-scale trials showed positive outcomes of SGLT2-inhibitors (SGLT2i) in elderly patients with CKD. Patients with Alport syndrome, a type IV collagen disease, develop CKD early in life. Whether the use of SGLT2i is safe and effective in patients with the type IV collagen disease Alport syndrome (and thus a different pathogenesis) has not yet been investigated specifically besides case reports. Method For the first time, this observational, multicenter, international study (NCT02378805) assessed 112 patients with AS from nine countries and 21 trial sites after start of SGLT2i at early stages of their chronic kidney disease (CKD). The study's primary endpoint was change of albuminuria in albumin/g creatinine after start of therapy with SGLT2i. Results Compared to the large randomized trials investigating the effect of SGLT2i in CKD, the adult patients in this trial were much younger (38 ± 14 years; n = 101), had a better eGFR (63 ± 35 ml/min/1.73m2; n = 98) and had a higher albuminuria (1699 ± 1472 mg/g creatinine; n = 51). At a mean time on SGLT2i-therapy of 6 ± 1 months, albuminuria decreased significantly (1727 ± 1564 vs. 1203 ± 1165 mg/g creatinine; n = 33; p = 0.01). Compared to baseline, at the first three follow-up visits after initiation of SGLT2i-therapy, a significant reduction of albuminuria >30% was observed. Mean loss of eGFR was 9 ± 12 ml/min/1.73 m² almost one year after initiation of SGLT2i-therapy (n = 35). At a mean follow up of 12 ± 2 month after initiation of SGLT2i-therapy, serum-albumin increased significantly from 3.7 ± 0.7 to 4.0 ± 0.4 g/dL (n = 18; p = 0.019). At a total of 68 patient-years at risk, adverse events occurred in 11/85 patients (13%). Two very serious adverse events (acute necrotizing pancreatitis and Fournier's gangrene) occurred. Conclusion This study demonstrated that SGLT2i, when added to RASi, have the potential to reduce the rate of albuminuria in adult patients with Alport Syndrome. The study will be continued to provide valuable data on the long-term course of CKD under SGLT2i-therapy in AS to investigate if the promising reduction of albuminuria results in a clinical relevant delay in renal failure. This observational study successfully formed the scientific basis for the current randomized controlled trial with SGLT2i in children and young adults with AS Double Protect Alport.