The present work was aimed to investigate using of potassium fertilizer as well as nano chitosan -NPK to alleviate the negative effect of water stress and its effect on cotton plant and some water relations. Two field experiments were conducted to study the possibility of using potassium fertilizer and nano chitosan -NPK to eliminate the negative impacts of water stress. The design of the experiment was split design plot, where number of irrigation treatments (6 and 9) were arranged in main plots, while potassium fertilization, i.e., K 1 = 96 kg K/ha as potassium sulphate, K 2 = 96 kg K/ha + twice foliar application of 2% potassium sulphate, K 3 = 96 kg K/ha + twice foliar application with 2% nano chitosan-NPK, K 4 = four times of foliar application with 2% potassium sulphate, and K 5 = four times of foliar application with 2% nano chitosan-NPK. The results obtained indicated that K 3 followed by K 2 which achieved the favourable values of plant height, first fruiting node, number of fruiting branches/plant, number of open bolls/plant, boll weight, seed index, lint percentage, seed cotton yield. Neither potassium fertilization nor irrigation number altered fiber properties. The data of the interaction showed the combined 96 kg K/ha as potassium sulphate + twice foliar application with 2% nano chitosan-NPK can diminish the negative effect of drought stress under deficit conditions, with higher seed cotton yield nearly equal to those obtained under full irrigation. It could be concluded that potassium fertilization and nano chitosan-NPK can improve cotton plant tolerance to water stress and enhance cotton productivity.