AIM: To compare ultra-widefield (24×20 mm2) swept-source optical coherence tomography angiography (SS-OCTA) and fluorescein angiography (FA) in the evaluation of diabetic retinopathy (DR) lesions. METHODS: Forty-six eyes of 23 patients with treatment-naïve DR were included at Peking University People’s Hospital from September 1, 2021, until December 31, 2021, as well as 23 age and gender matched healthy controls. Quantitative assessments of DR lesions on FA and SS-OCTA (superficial capillary plexus, SCP, 24×20 mm2) were performed. RESULTS: Area of fovea avascular zone (FAZ) was larger in DR cases than controls (0.34±0.069 mm2 vs 0.287±0.108 mm2, P=0.006). In DR eyes, the mean FAZ area was 0.34±0.069 and 0.334±0.087 mm2 on SS-OCTA and FA, respectively (P=0.428), while the median FAZ perimeter was 2.382 (IQR, 2.201-2.59) and 2.333 (IQR, 2.138-2.6) mm on SS-OCTA and FA images (P=0.733). There was no significant difference in the size of the non-perfusion area (NPA) between the images on SS-OCTA and FA (12.389, IQR 4.96-28.3 and 11.125, IQR 5-28.31 mm2, P=0.197). The median total microaneurysm (MA) count was 35 (IQR, 19-46) and 73 (IQR, 43-93) on SS-OCTA and FA (P<0.001), respectively. No significant difference in intra-retinal microvascular abnormality (IRMA) and neovascularization (NV) count was found between the two techniques. The intraclass coefficient (ICCs) of all the parameters above indicated stable repeatability. CONCLUSION: Ultra-widefield SS-OCTA represents a reliable, noninvasive, and quantitative imaging technique in the assessment of microvasculature in DR, which offers a potential substitute for FA in DR evaluation.