Field experiment was conducted at Mattana Research Station, Qena Governorate to investigate the effect of foliar and soil application of potassium fertilizer on yield and quality of plant cane planted in 1996/1997 season and its first and second ratoons grown in 1997198 and1998/99 seasons. Each field trial included twelve treatments of po­tassium fertilization represented the combination between three levels as foliar application (untreated (control), liquid potassium (35.2% K20) at rate of 0.2% (I L/500 L water per feddan) and potassium sulphate (48% K20) at rate of 2% (10 kg K20/500 L water per feddan)) and four levels as soil application (0, 24, 48, and 72 kg K20/fed). A split plot design in four replicats was used where foliar application of potas­sium was allocated in the main plots while soil application of potassium was randomly distributed in the sub plots. Results obtained showed that foliar application significantly increased cane yield, sugar yield, sucrose % and glucose % in the plant cane and 2nd ratoon while in the 1st ra­coon, there was a significant increase for cane yield, purity % and glu­cose % due to the foliar application. Concerning the soil application of K fertilizer, sugar yield and sucrose % were not significantly affected by K-levels as soil application in the plant cane, 1st and 2nd ratoons except cane yield and p...rity % in the 1st ratoon and glucose % in the 2nd ra­toon which were significantly enhanced by soil application of K fertilizer. Generally, increasing K-level as foliar or soil application slightly increased the yield and quality of sugar cane variety G 54-C9.