Abstract: A pot experiment was conducted in a glasshouse at National Agricultural Research Center (NARC), Islamabad to study the effect of potash levels viz. 100 and 200 K 2 O ha 1 on Nitrogen, phosphorus, Potassium, chlorophyll and protein content of young mature leaves at flower initiation stage (50 days after seeding) in three resistant cotton varieties namely CIM443, CIM109, CIM446 during the year 1999. Potassium content was significantly increased with increasing K2O levels and it was maximum at 200 kg K2O ha-1 in all the varieties. Nitrogen content of young mature leaves decreased significantly with increasing K2O levels while protein content of young mature leaves increased significantly with increasing K2O levels and overall maximum increase of 37.5% was observed at 200 kg K2O ha-1. Phosphorus content of young mature leaves increased significantly with potash application and it was maximum at 100 kg K2O ha-1. In conclusion, application of potash did not affect the leaf chlorophyll content but significant differences in leaf chlorophyll content of different varieties were observed. However, an increase of 15.63% in leaf chlorophyll content was found with addition of 200 kg K2O ha-1.