This research was held during 2020 and 2021 seasons in a private vineyard in Menoufia governorate, Egypt; with the goal of improving the quality of King Ruby grape and controlling gray mold disease (Botrytis cinerea P.) using different potassium salts as monopotassium phosphate (MKP), dipotassium phosphate (DKP), and tripotassium phosphate (TKP). Four sprays of each salt, at 1% and 3% doses were applied every 15 days, starting after fruit set and ending two weeks before harvest. The three potassium salts were effective in enhancing yield and both physical and chemical properties significantly, however, firmness and adherence slightly declined with increasing K element concentration. After a month of cold storage, a clear deterioration occurred; but the salts' treatments, especially TKP, still performing better than the control in all aspects definitely showing the least cluster weight loss and berry decay compared to the control, in both seasons of the study. As for the In vitro study, it reveal that the three salts significantly reduced the growth of Botrytis pathogenic fungus than the control; especially TKP, showed the highest mycelium growth reduction. Furthermore, DKP had stronger inhibition effect than MKP. In conclusion, the three potassium phosphate salts have the potential to improve grape yield, quality, and prevent gray mold infection, making them safe growth promoters and fungicides, especially TKP at 3%.