Two field experiments were carried out at Gemmeiza Agricultural Research station, El-Gharbia Governorate during 2008 and 2009 seasons. The investigation aimed to study the effect of foliar application of phosphoric acid (P2O5 85 %) at 1, 1.5 and 2 cm3/ L and spraying mepiquat chloride (Pix) 50 g/fed. at 1, 2 and 3 cm3/ L at pinhead square, start of flowering and peak of flowering stage on the productivity of cotton plants (Giza 86) . The obtained results showed that, in comparison with the control, phosphorus and Pix tended to decrease plant height. On the other hand, these treatments, in general increased number of fruiting branches / plant, number of open bolls / plant, boll weight, seed cotton yield per fed., relative fruitfulness (R.F.), earliness %, also increased leaves contents of chlorophyll a, b and (a + b), carotenoids, total phenol and poly phenol as well as oil and protein contents in seeds. These treatments did not affect lint %, seed index and fiber properties in both seasons. The highest values obtained from foliage spraying of cotton plants with (PHX 1.5 cm3/ L phosphorus and 2 cm3/ L Pix) at flowering stage improved performance and yield of cotton plants.