Two field experiments were carried out in the farm of Faculty of Applied Science, Hadhramout University, Seiyun during two consecutive growing seasons of 2001/2002 and 2002/2003 to study the effect of Potassium fertilization on the growth and yield of potatoes. Each experiment contained four levels.( control .90, 180, 270 kg K2 SO4 / ha ) in a randomized complete block design (RCBD) with four replications .The Statistical analysis showed that there were no significant differences in the studied characteristics, such as plant growth and yield at the 5% level (F-test). It could be concluded that application of Potassium fertilizer was ineffective on growth and yield of potatoes var . Diamont under that soil conditions in Seiyun Governorate, Yemen