The present investigation was carried out at Shandaweel Agricultural Research Station during 2005 and 2006 seasons on Egyptian cotton cultivar Giza 90. (Gossypinm barbadense L.) to study the effect of Potassium  Sulphate  application methods and timing on growth and seed cotton yield as well as yield components. A randomized complete block design with four replicates was used six treatments were as follows: K₀: Without Potassium application (control). K_1: Potassium Sulphate (48 %K₂O) was applied at sowing. K_2: Potassium Sulphate (48%K₂O) was applied at thinning date. K₃: Folair spraying with Potassium Sulphate (48 %K₂O) twice at budding and flowering stages.  K₄: Folair spraying with Potassium Sulphate (48%K₂O) three times at budding stage, beginning of flowering and 15 days later.  K₅: Folair spraying with citrate (Potassium -p 45% citrate) twice at budding and flowering stages.  The results of these experiments indicated that plant height at harvest, Number of fruiting branches plant, number of open bolls/plant, boll weight, seed cotton yield/plant and faddan were significantly increased by tested treatments in both seasons. While, height of first fruiting node and number of plants at harvest were not affected by tested treatments.