This study was carried out during the two successive seasons 2022 and 2023 on 15-years-old “Thompson seedless grapes” grown at Assiut governorate, Egypt, to study the effect of four foliar spray treatments: control (spraying with water, T1), potassium nitrate (36% K₂O, T2), potassium citrate (40% K₂O, T3), and potassium thiosulfate (36% K₂O, T4) as preharvest on yield, berry quality, storability quality parameters, and enzyme activity of Thompson Seedless Grapes. All vines were sprayed three times during the growing season (end of May, mid-June, and first of July). Treated clusters were stored at 2±2°C and 85-90% RH for 5 weeks. The results showed that all treatments significantly improved the quantity and quality at harvest of “Thompson Seedless Grapes” potassium citrate or potassium thiosulfate treatment at 0.2% K₂O increased cluster weight, yield (kg/vine) and yield (ton/ha), berry weight, and berry diameter, while potassium nitrate increased leaf area (cm²), juice weight %. Throughout cold storage at 2±2°C and 85-90% RH for 5 weeks, foliar application of different sources of potassium decreased weight loss %, shattering %, decay %, total loss % and maintained quality and increased antioxidant enzyme activities in the end storage period. The best potassium spray treatments were potassium citrate or potassium thiosulfate to improve the yield and quality at harvest, as well as reduce weight loss, shattering %, decay %, total loss % and the best quality during storage.