Research to delineate nitrogen, potassium, and mepiquat chloride (MC) effects on cotton performance has been primarily conducted with upland cotton (Gossypium hirsutum L.). A field study was conducted at the Agricultural Research Center, Giza, Egypt, to evaluate N, K, and MC effects on yield, yield components, and fiber properties of Egyptian cotton (Gossypium barbadense L). The experimental treatments were N rates of 95 or 143 kg ha-1, foliar K at 0.0, 319, 638, or 957 g ha-1 applied 70 and 95 days after planting, and MC applied 75 days after planting at 0.0 or 48 g ha-1, and 90 days after planting at 0.0 and 24 g ha-1. Number of opened bolls per plant, boll weight, seed index, lint index, seed cotton yield per plant, and seed cotton and lint yield per hectare increased with the higher N rate and with foliar application of K and MC. There were no interactions among N, K, and MC on yield, and applications increased average lint yield 125 kg ha-1. Effect on earliness of harvest was inconsistent, and harvest maturity increased from 69% to 72% with application of K and MC in the second season. Nitrogen, K, and MC effects on fiber properties were small and inconsistent. The combination of the three inputs increased length 0.3 mm, micronaire 0.1 units, and strength 0.39 cN tex-1 (0.4 g tex-1). Under the conditions of this study, applying N at 143 kg ha-1 combined with foliar application of K at 319 g ha-1 and MC at 48 + 24 g ha-1 improved growth and yield of Egyptian cotton.