Two field experiments were carried out at El-Gemmeiza Agricultural Research Station, El-Gharbia Governorate in 2014 and 2015 seasons, to study the effect of nano-fertilizer (Lithovit) rates (0, 2.5, 5 and 7.5 g/l) and foliar potassium fertilizer (in the form of  Potasin-P) rates (2.5, 5 and 7.5 cm³/l) under three planting dates (8 April, 8 May and 8 June) on leaves chemical composition of the Egyptian cotton (Gossypium barbadense L.), cultivar Giza 86. Cotton plants were foliar sprayed with Lithovit and Potasin-P at 45 and 60; 46 and 61 days after planting, respectively. Leaves N, P, K, chlorophyll a, b, total chlorophyll, carotenoids and total carbohydrates contents were significantly affected by planting date in both seasons, in favour of early planting date (8 April) compared to medium and late planting dates (8 May and 8 June). Delaying planting date significantly increased leaf proline content and leaf peroxidase activity which indicate the presence of heat stress effect on the plant.Leaves N, chlorophyll a, b, total chlorophyll, carotenoids and total carbohydrates contents were significantly affected by rates of Potasin-P in both seasons, in favour of the medium rate of Potasin-P (5cm³/l). While, leaves P and K contents were significantly increased by using the high rate of Potasin-P (7.5cm³/l). The medium rate of Potasin-P (5cm³/l) significantly decreased leaf proline content and peroxidase activity which indicate favorable plant conditions.Leaves N, P, K, chlorophyll a, b, total chlorophyll, carotenoids and total carbohydrates contents were significantly increased by each increment of nano-fertilizer (Lithovit). The inverse was true in leaf proline content and peroxidase activity. The decrease in these traits induced favorable plant conditions and reflected on reduce environmental stress effect.The second order interaction had a significant effect on all studied chemical composition of leaves. Cotton plants sown on 8 April and sprayed with 5cm³ Potasin-P /l and 7.5 g Lithovit/l recorded the highest values of N, P, K, chlorophyll a, b, total chlorophyll, carotenoids and total carbohydrates content in leaves. In the contrary, this interaction recorded the lowest values of leaf proline content and peroxidase activity which induced favorable plant conditions and reflect on reduce environmental stress effect. It can be concluded that the mentioned interaction was the recommended treatment for optimum chemical composition of cotton leaves under experimental conditions.