TWO FIELD experiments were conducted at the Farm of Sids Agricultural Research Station, ARC, Egypt, during 2016 and 2017 seasons to study the response of cotton to potassium fertilization (12, 24, 36 and 48kg K2O) as soil application as well as 5kg K2O/fad as foliar spraying three times at squaring, beginning of flowering and top of flowering) under different irrigation intervals at recommended irrigation interval (every 12 days), every 15 days, every 18 days and every 21 days). The results show that increasing potassium fertilization up to 36kg or 48kg K2O/fad as soil application as well as decreasing irrigation interval to 12 days exhibited the highest values of plant height, number of fruiting branches/ plant, number of open polls/plant, seed cotton yield, earliness % and seed index as well as leaf content of N, K, chlorophyll A and B and carotenoids. On the other hand, lint percentage and fiber properties did not respond to either potassium or irrigation treatments, while P content increased as increasing water irrigation. Increasing both potassium levels and the irrigation intervals improved water use efficiency and water utilization efficiency. The results of the interaction between potassium and irrigation treatments reveal that irrigation cotton plants every 15 days when fertilized with 48kg K2O/fad as soil application produced highest growth, yield and its components and chemical content of cotton leaf equal to these irrigated every 12 days and supplied water 36 or 48kg K2O/fad.