Four field experiments were carried out at El-Serw Agricultural Research Station of Damietta Governorate and Kafer El-Hamam Agricultural Research Station. Sharkia Governorate during 2004 and 2005 seasons to study the effect of two levels of potassium fertilizer (12.5 and 25kg K₂O fed.^-1) added as a soil application companied with one or two foliar spray of 2% soluble potassium sulphate (50% K₂O) (solupotasse) on cotton yield, yield component and quality of seeds. The results revealed that potassium treatments increased number of open bolls / plant, boll weight /gm, seed cotton yield (ton fed.^-1), lint percentage and a slight increase in oil percentage, but it had insignificant effect on seed index and protein percentage comparing to control treatment. The addition of 12.5 kg k₂O fed.^-1 after thinning as soil application + two foliar sprays, with 2% soluble potassium sulphate (solopotasse) at budding stage (45 days after sowing) and before flowering is considered to be a recommended amounts for cotton (3.29 ton fed.^-1) at El-Serw area, while addition of 25kg k₂O fed.^-1as a soil application + two sprays of 2% soluble potassium sulphate solopotasse at the      above mentioned time was the recommended amounts in Kafer El-Hamam site.  which yielded (3.34 ton fed.^-1).